Structures for supporting porous electrode elements

ABSTRACT

A catheter assembly comprising a elongated, flexible support structure having an axis. The assembly also includes an elongated porous electrode assembly carried by the support structure along the axis for contact with tissue. The elongated porous electrode assembly comprises a wall having an exterior peripherally surrounding an interior area, a lumen to convey a medium containing ions into the interior area, and an element coupling the medium within the interior area to a source of electrical energy. At least a portion of the wall comprising a porous material is sized to allow passage of ions contained in the medium to thereby enable ionic transport of electrical energy through the porous material to the exterior of the wall to form a continuous elongated lesion pattern in tissue contacted by the wall. The support structure can have a curvilinear geometry, e.g., a loop shape, and the elongated porous electrode assembly conforms to the curvilinear geometry.

FIELD OF THE INVENTION

[0001] The invention generally relates structures for supporting one ormore diagnostic or therapeutic elements in contact with body tissue. Ina more particular sense, the invention relates to structures well suitedfor supporting one or more electrode elements within the heart.

BACKGROUND OF THE INVENTION

[0002] The treatment of cardiac arrhythmias requires electrodes capableof creating tissue lesions having a diversity of different geometriesand characteristics, depending upon the particular physiology of thearrhythmia to be treated.

[0003] For example, it is believed the treatment of atrial fibrillationand flutter requires the formation of continuous lesions of differentlengths and curvilinear shapes in heart tissue. These lesion patternsrequire the deployment within the heart of flexible ablating elementshaving multiple ablating regions. The formation of these lesions byablation can provide the same therapeutic benefits that the complexincision patterns that the surgical maze procedure presently provides,but without invasive, open heart surgery.

[0004] By way of another example, small and shallow lesions are desiredin the sinus node for sinus node modifications, or along the A-V groovefor various accessory pathway ablations, or along the slow zone of thetricuspid isthmus for atrial flutter (AFL) or AV node slow pathwaysablations. However, the elimination of ventricular tachycardia (VT)substrates is thought to require significantly larger and deeperlesions.

[0005] There also remains the need to create lesions having relativelylarge surface areas with shallow depths.

[0006] The task is made more difficult because heart chambers vary insize from individual to individual. They also vary according to thecondition of the patient. One common effect of heart disease is theenlargement of the heart chambers. For example, in a heart experiencingatrial fibrillation, the size of the atrium can be up to three timesthat of a normal atrium.

[0007] A need exists for electrode support structures that can createlesions of different geometries and characteristics, and which canreadily adopt to different contours and geometries within a body region,e.g., the heart.

SUMMARY OF THE INVENTION

[0008] The invention provides structures for supporting operativetherapeutic or diagnostic elements within an interior body region, likethe heart. The structures possess the requisite flexibility andmaneuverability permitting safe and easy introduction into the bodyregion. Once deployed in the body region, the structures possess thecapability to conform to different tissue contours and geometries toprovide intimate contact between the operative elements and tissue.

[0009] In one embodiment, the invention provides a catheter assemblycomprising a elongated, flexible support structure having an axis. Theassembly also includes an elongated porous electrode assembly carried bythe support structure along the axis for contact with tissue. Theelongated porous electrode assembly comprises a wall having an exteriorperipherally surrounding an interior area, a lumen to convey a mediumcontaining ions into the interior area, and an element coupling themedium within the interior area to a source of electrical energy. Atleast a portion of the wall comprising a porous material is sized toallow passage of ions contained in the medium to thereby enable ionictransport of electrical energy through the porous material to theexterior of the wall to form a continuous elongated lesion pattern intissue contacted by the wall.

[0010] In one embodiment, the elongated porous electrode assemblycomprises an array of electrode, segments formed by segmenting the wallalong the axis.

[0011] In one embodiment, the support structure has a curvilineargeometry, and the elongated porous electrode assembly conforms to thecurvilinear geometry.

[0012] In one embodiment, the support structure is adapted to form aloop geometry, and the elongated porous electrode assembly conforms tothe loop geometry.

[0013] Other features and advantages of the inventions are set forth inthe following Description and Drawings, as well as in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view of a probe, which carries on itsdistal region a multiple electrode support structure that embodiesfeatures of the invention;

[0015]FIG. 2A is an enlarged side view, with portions broken away and insection, of the distal region of the probe shown in FIG. 1;

[0016]FIG. 2B is a side view of the multiple electrode structure shownin FIG. 1, in which stiffness is varied using a slidable, tapered splineleg;

[0017]FIG. 3A is an enlarged side view of the distal region of the probeshown in FIG. 1, showing the multiple electrode structure advanced fromthe associated sheath to form a loop;

[0018]FIG. 3B is a perspective end view of an embodiment of the sheathshown in FIG. 3A, in which wires are placed to provide added torsionalstiffness;

[0019]FIG. 3C is an end view of an embodiment of the sheath shown inFIG. 3A, which has been eccentrically extruded to provide addedtorsional stiffness;

[0020]FIG. 4A is a side view of the distal region shown in FIG. 3A, inwhich the catheter tube is stiffer than the sheath, and in which thecatheter tube has been rotated within the sheath and flipped over uponitself;

[0021]FIG. 4B is a side view of the distal region shown in FIG. 3A, inwhich the catheter tube is not as stiff as the sheath, and in which thecatheter tube has been rotated within the sheath to form an orthogonalbend in the loop;

[0022]FIG. 5 is a side view of an embodiment of the distal region shownin FIG. 3A, in which the size of the slot through which the loop extendscan be varied;

[0023]FIG. 6 is a side view of an embodiment of the distal region shownin FIG. 3A, in which a prestressed spline within the loop structurealters the geometry of the structure;

[0024]FIGS. 7A, 7B, and 7C are top views of different embodiments of thedistal region shown in FIG. 3A, in which the slot is shown havingdifferent geometries, which affect the geometry of the resulting loop;

[0025]FIG. 8 is a side view of an embodiment of the distal region shownin FIG. 3A, in which the proximal end of the slot is tapered tofacilitate formation of the loop;

[0026]FIG. 9 is a side view of an embodiment of the distal region shownin FIG. 3A, in which the slot has a helical geometry;

[0027]FIG. 10 is a side view of the distal region shown in FIG. 9, withthe loop support structure deployed through the helical slot;

[0028]FIG. 11 is a side view of an embodiment of the distal region shownin FIG. 3A, with the catheter tube having a prebent geometry orthogonalto the loop structure;

[0029]FIG. 12 is a side view of an embodiment of the distal region shownin FIG. 11, with the sheath advanced forward to straighten the prebentgeometry;

[0030]FIG. 13A is a section view of the catheter tube within the sheath,in which the geometries of the sheath and catheter tube are extruded toprevent relative rotation;

[0031]FIG. 13A is a section view of the catheter tube within the sheath,in which the geometries of the sheath and catheter tube are extruded topermit limited relative rotation;

[0032]FIG. 14 is an enlarged side view of an alternative embodiment thedistal region of the probe shown in FIG. 1;

[0033]FIG. 15A is a side view of the distal region shown in FIG. 14,showing the multiple electrode structure advanced from the associatedsheath to form a loop;

[0034]FIG. 15B is a side view of an alternative embodiment of the distalregion shown in FIG. 14;

[0035]FIGS. 16A, 16B, and 16C are view of the distal region shown inFIG. 14, showing alternative ways to stiffen the flexible junctionbetween the sheath and the catheter tube;

[0036]FIG. 17A is an enlarged side view of an alternative embodiment thedistal region of the probe shown in FIG. 1;

[0037]FIG. 17B is a section view of an embodiment of the distal regionshown in FIG. 17A;

[0038]FIGS. 18, 19, and 20, are side sectional view, largelydiagrammatic, showing an embodiment of the distal region shown in FIG.1, in which the electrode array is movable;

[0039]FIG. 21 is an enlarged side view of an alternative embodiment ofthe distal region of the probe shown in FIG. 1, with the associatedsheath withdrawn and with no rearward force applied to the associatedpull wire;

[0040]FIG. 22 is an enlarged side view of the distal region of the probeshown in FIG. 21, with the associated sheath advanced;

[0041]FIG. 23 is an enlarged side view of distal region of the probeshown in FIG. 21, with the associated sheath withdrawn and with rearwardforce applied to the associated pull wire to form a loop structure;

[0042]FIG. 24 is an enlarged side view of an alternative embodiment ofthe distal region shown in FIG. 21, with a pivot connection;

[0043]FIG. 25 is an enlarged elevation side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed loop structure;

[0044]FIG. 26 is an enlarged, side section view of the slidable end capshown in FIG. 25;

[0045]FIG. 27 is a side view of the distal region shown in FIG. 25, withthe interior wire pulled axially to change the geometry of the preformedloop structure;

[0046]FIG. 28 is a side view of the distal region shown in FIG. 25, withthe interior wire bend across its axis to change the geometry of thepreformed loop structure;

[0047]FIG. 29 is a side view of the distal region shown in FIG. 25, withthe interior wire rotated about its axis to change the geometry of thepreformed loop structure;

[0048]FIGS. 30 and 31 are side views of the distal region shown in FIG.25, with the location of the slidable cap moved to change the geometryof the preformed loop structure;

[0049]FIG. 32 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed, multiple spline loop structure;

[0050]FIG. 33 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 32 showing apreformed, multiple spline loop structure with asymmetric mechanicalstiffness properties;

[0051]FIG. 34 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed, multiple independent spline loop structures;

[0052]FIG. 35 is an enlarged elevation side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed loop structure, which, upon rotation, forms an orthogonalbend;

[0053]FIG. 36 is an enlarged side view of the distal region shown inFIG. 35 with the orthogonal bend formed;

[0054]FIG. 37 is a section view of the distal region shown in FIG. 35,taken generally along line 37-37 in FIG. 35,

[0055]FIG. 38 is a section view of the distal region shown in FIG. 35,taken generally along line 38-38 in FIG. 35

[0056]FIG. 39 is a section view of the distal region shown in FIG. 36taken generally along line 39-39 in FIG. 36

[0057]FIG. 40 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apretwisted loop structure, which forms an orthogonal bend;

[0058]FIG. 41 is a side section views of a portion of the loop structureshown in FIG. 40, taken generally along line 41-41 in FIG. 40

[0059]FIG. 42A is an enlarged side view of an alternative embodiment ofthe distal region of the probe shown in FIG. 1, showing a preformed loopstructure, which, upon rotation, forms an orthogonal bend;

[0060]FIG. 42B is an enlarged side view of the distal region shown inFIG. 42A, with the orthogonal bend formed;

[0061]FIG. 43 is an enlarged side perspective view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed loop structure, which has a prestressed interior splineforming an orthogonal bend;

[0062]FIG. 44 is a largely diagrammatic view of the deployment of thedistal region of the probe shown in FIG. 1 in the right atrium of aheart;

[0063]FIG. 45 is a side elevation view of an alternative embodiment ofthe distal region of the probe shown in FIG. 1, showing aself-anchoring, multiple electrode structure;

[0064]FIG. 46 is a section view of the self-anchoring structure shown inFIG. 45

[0065]FIG. 47 is a side elevation view of an embodiment of the distalregion shown in FIG. 48 in which the anchoring branch is movable;

[0066]FIG. 48 Is a side elevation view of the distal region of the probeshown in FIG. 45 with the self-anchoring, multiple electrode structurewithdrawn within an associated sheath;

[0067] FIGS.,49A, 49B, and 49C show the deployment of the multiple,self-anchoring electrode structure shown in FIG. 45 within a bodyregion;

[0068]FIGS. 50A and 50B show, in diagrammatic form, the location ofregions within the heart in which the self-anchoring structure shown inFIG. 45 can be anchored;

[0069]FIG. 51 is a side view of an embodiment of the self-anchoringstructure shown in FIG. 45 in which the branch carrying electrodeelements can be advanced or retracted or rotated along or about itsaxis;

[0070]FIG. 52 is a side view of an embodiment of the self-anchoringstructure shown in FIG. 45 in which the branch carrying electrodeelements can be torqued about the main axis of the structure;

[0071]FIG. 53 is a side elevation view of an alternative embodiment ofthe distal region of the probe shown in FIG. 1, showing aself-anchoring, loop structure;

[0072]FIG. 54 is a side elevation view of an alternative embodiment ofthe distal region shown in FIG. 54 also showing a type of aself-anchoring, loop structure;

[0073]FIG. 55 is a side elevation view of an alternative embodiment ofthe distal region shown in FIG. 45 showing a self-anchoring structurewith an active anchoring element;

[0074]FIG. 56 is a side view of an alternative embodiment of the distalregion of the probe shown in FIG. 1, showing a spanning branchstructure;

[0075]FIG. 57 is a side sectional view of the spanning branch structureshown in FIG. 56, with the associated sheath advanced;

[0076]FIG. 58 is a side view of the spanning branch structure shown inFIG. 56, with the associated sheath retracted and the structure deployedin contact with tissue;

[0077]FIG. 59 is a side view of an alternative embodiment a spanningbranch structure of the type shown in FIG. 56;

[0078]FIG. 60 is a side view of the spanning branch structure shown inFIG. 59 deployed in contact with tissue;

[0079]FIG. 61 is a side view of an alternative embodiment of the distalregion of the probe shown in FIG. 1, showing a spring-assisted, spanningbranch structure;

[0080]FIG. 62 is a side sectional view of the spring-assisted, spanningbranch structure shown in FIG. 61, with the associated sheath advanced;

[0081]FIGS. 63A and 63B are side views of the deployment in a bodyregion of the spring-assisted, spanning branch structure shown in FIG.61;

[0082]FIG. 63C is a side view a spring-assisted, spanning branchstructure, like that shown in FIG. 61, with an active tissue anchoringelement;

[0083]FIG. 64 is a representative top view of long, continuous lesionpattern in tissue;

[0084]FIG. 65 is a representative top view of segmented lesion patternin tissue;

[0085]FIG. 66 is a side view of an alternative embodiment of aself-anchoring, loop structure, showing the catheter tube detached fromthe associated sheath;

[0086]FIG. 67 is a side view of the self-anchoring, loop structure shownin FIG. 66, with the catheter tube attached to the associated sheath;

[0087]FIG. 68 is a side view of the self-anchoring, loop structure shownin FIG. 67, showing the catheter tube advanced in an outwardly bowedloop shape from the associated sheath;

[0088]FIG. 69 is a side section view of a portion of the distal regionshown in FIG. 66, showing the inclusion of a bendable spring to steerthe self-anchoring loop structure;

[0089]FIG. 70 is a side view of the self-anchoring, loop structure shownin FIG. 67, showing the structure deployed for use within a body cavity;

[0090]FIG. 71 is a side view, with parts broken away and in section, ofan alternative embodiment of the self-anchoring, loop structure shown inFIG. 67, with an interference fit releasably coupling the catheter tubeto the associated sheath;

[0091]FIG. 72 is a side view, with parts broken away and in section, ofan alternative embodiment of the self-anchoring, loop structure shown inFIG. 67, with a releasable snap-fit coupling the catheter tube to theassociated sheath;

[0092]FIG. 73 is a side view of an alternative embodiment of theself-anchoring, loop structure shown in FIG. 67, with a pivotingconnection releasably coupling the catheter tube to the associatedsheath;

[0093]FIG. 74 is a side view of a embodiment of a pivoting connection ofthe type shown in FIG. 73, with the catheter tube released from theassociated sheath;

[0094]FIG. 75 is a side view, with parts broken away and in section, thepivoting connection shown in FIG. 74, with the catheter tube attached tothe associated sheath;

[0095]FIG. 76 is a side perspective view of the pivoting, connectionshown in FIG. 75, with the catheter tube pivoting with respect to theassociated sheath;

[0096]FIG. 77A is an exploded, perspective view of an alternativeembodiment of a releasable pivoting connection of the type shown in FIG.73, with the catheter tube detached from the associated sheath;

[0097]FIG. 77B is an exploded, perspective view of the reverse side ofthe pivoting connection shown in FIG. 77A, with the catheter tubedetached from the associated sheath;

[0098]FIG. 77C is a top side view of the releasable pivoting connectionshown in FIG. 77A, with the catheter tube attached to the associatedsheath;

[0099]FIG. 77D is a top side view of the releasable pivoting connectionshown in FIG. 77C, with the catheter tube attached to the associatedsheath and pivoted with respect to the sheath;

[0100]FIG. 78A is an exploded, perspective view of an alternativeembodiment of a releasable pivoting connection of the type shown in FIG.73, with the catheter tube detached from the associated sheath;

[0101]FIG. 78B is a top view of the releasable pivoting connection shownin FIG. 78A, with the catheter tube attached to the associated sheath;

[0102]FIG. 78C is a top side view of the releasable pivoting connectionshown in FIG. 78B, with the catheter tube attached to the associatedsheath and pivoted with respect to the sheath;

[0103]FIG. 79 shows, in diagrammatic form, sites for anchoring aself-anchoring structure within the left or right atria;

[0104]FIGS. 80A to 80D show representative lesion patterns in the leftatrium, which rely, at least in part, upon anchoring a structure withrespect to a pulmonary vein;

[0105]FIGS. 81A to 81C show representative lesion patterns in the rightatrium, which rely, at least in part, upon anchoring a structure withrespect to the superior vena cava, the inferior vena cava, or thecoronary sinus;

[0106]FIG. 82 shows a loop structure of the type shown in FIG. 34A,which carries a porous ablation element;

[0107]FIG. 83 is a side section view of the porous ablation elementtaken generally along line 83-83 in FIG. 82;

[0108]FIG. 84 is a side section view of an alternative embodiment of theporous ablation element, showing segmented ablation regions, takengenerally along line-84-84 in FIG. 85;

[0109]FIG. 85 is an exterior side view of the segmented ablation regionsshown in section in FIG. 84;

[0110]FIG. 86 is a side section view of an alternative embodiment of aporous electrode element of the type shown in FIG. 82;

[0111]FIG. 87 is a side view of a probe, like that shown in FIG. 1, thatincludes indicia for marking the extent of movement of the catheter tuberelative to the associated sheath;

[0112]FIG. 88 is a side view of an alternative embodiment of a probe, ofthe type shown in FIG. 1, showing indicia for marking the extent ofmovement of the catheter tube relative to the associated sheath;

[0113]FIG. 89 is a side sectional view of a catheter tube having amovable steering assembly;

[0114]FIG. 90 is an elevated side view of a preformed loop structurehaving a movable steering mechanism as shown in FIG. 89;

[0115]FIG. 91 is a section view of the loop structure shown in FIG. 90,taken generally alone line 91-91 in FIG. 90;

[0116]FIG. 92 is an elevated side view of using the movable steeringmechanism shown in FIG. 89 to change the geometry of the loop structureshown in FIG. 90; and

[0117]FIG. 93 is an elevated side view of using two movable steeringmechanisms, as shown in FIG. 89, to change the geometry of a loopstructure.

[0118] The invention may be embodied in several forms without departingfrom its spirit or essential characteristics. The scope of the inventionis defined in the appended claims, rather than in the specificdescription preceding them. All embodiments that fall within the meaningand range of equivalency of the claims are therefore intended to beembraced by the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] This Specification discloses various multiple electrodestructures in the context of catheter-based cardiac ablation. That isbecause the structures are well suited for use in the field of cardiacablation.

[0120] Still, it should be appreciated that the disclosed structures areapplicable for use in other applications. For example, the variousaspects of the invention have application in procedures requiring accessto other regions of the body, such as, for example, the prostrate,brain, gall bladder, and uterus. The structures are also adaptable foruse with systems that are not necessarily catheter-based.

[0121] I. Flexible Loop Structures

[0122] A. Slotted Jointed Sheath

[0123]FIG. 1 shows a multiple electrode probe 10 that includes astructure 20 carrying multiple electrode elements 28.

[0124] The probe 10 includes a flexible catheter tube 12 with a proximalend 14 and a distal end 16. The proximal end 14 has an attached handle18. The multiple electrode structure 20 is attached to the distal end 16of the catheter tube 14 (see FIG. 2A).

[0125] The electrode elements 28 can serve different purposes. Forexample, the electrode elements 28 can be used to sense electricalevents in heart tissue. Alternatively, or in addition, the electrodeelements 28 can serve to transmit electrical pulses to measure theimpedance of heart tissue, to pace heart tissue, or to assess tissuecontact. In the illustrated embodiment, the principal use of theelectrode elements 28 is to transmit electrical energy, and, moreparticularly, electromagnetic radio frequency energy, to ablate hearttissue.

[0126] The electrode elements 28 are electrically coupled to individualwires (not shown in FIG. 1, but which will be discussed in greaterdetail later) to conduct ablating energy to them. The wires from thestructure 20 are passed in conventional fashion through a lumen in thecatheter tube 12 and into the handle 18, where they are electricallycoupled to a connector 38 (see FIG. 1). The connector 38 plugs into asource of RF ablation energy.

[0127] As FIG. 2A shows, the support structure 20 comprises a flexiblespline leg 22 surrounded by a flexible, electrically nonconductivesleeve 32. The multiple electrodes 28 are carried by the sleeve 32.

[0128] The spline leg 22 is preferably made from resilient, inert wire,like Nickel Titanium (commercially available as Nitinol material) or17-7 stainless steel. However, resilient injection molded inert plasticcan also be used. Preferably, the spline leg 22 comprises a thin,rectilinear strip of resilient metal or plastic material. Still, othercross sectional configurations can be used.

[0129] The spline leg 22 can decrease in cross sectional area in adistal direction, by varying, e.g., thickness or width or diameter (ifround), to provide variable stiffness along its length. Variablestiffness can also be imparted by composition changes in materials or bydifferent material processing techniques.

[0130] As FIG. 2B shows, the stiffness of the support structure 20 canbe dynamically varied on the fly by providing a tapered wire 544slidably movable within a lumen 548 in the structure 20. Movement of thetapered wire 544 (arrows 546 in FIG. 2B) adjusts the region of stiffnessalong the support structure 20 during use.

[0131] The sleeve 32 is made of, for example, a polymeric, electricallynonconductive material, like polyethylene or polyurethane or PEBAX™material (polyurethane and nylon). The signal wires for the electrodes28 preferably extend within the sleeve 32.

[0132] The electrode elements 28 can be assembled in various ways. Theycan, for example, comprise multiple, generally rigid electrode elementsarranged in a spaced apart, segmented relationship along the sleeve 32.The segmented electrodes can each comprise solid rings of conductivematerial, like platinum, which makes an interference fit about thesleeve 32. Alternatively, the electrode segments can comprise aconductive material, like platinum-iridium or gold, coated upon thesleeve 32 using conventional coating techniques or an ion beam assisteddeposition (IBAD) process.

[0133] Alternatively, the electrode elements 28 can comprise spacedapart lengths of closely wound, spiral coils wrapped about the sleeve 32to form an array of generally flexible electrode elements 28. The coilsare made of electrically conducting material, like copper alloy,platinum, or stainless steel, or compositions such as drawn-filledtubing. The electrically conducting material of the coils can be furthercoated with platinum-iridium or gold to improve its conductionproperties and biocompatibility.

[0134] The electrode elements 28 can also comprise porous materials,which transmit ablation energy through transport of an electrified ionicmedium. Representative embodiments of porous electrode elements 28 areshown in FIGS. 82 to 85, and will be described in greater detail later.

[0135] The electrode elements 28 can be operated in a uni-polar mode, inwhich the ablation energy emitted by the electrode elements 28 isreturned through an indifferent patch electrode 420 (see FIG. 44)externally attached to the skin of the patient. Alternatively, theelements 28 can be operated in a bi-polar mode, in which ablation energyemitted by one or more electrode element 28 is returned through anelectrode element 28 on the structure 20 (see FIG. 3A).

[0136] The diameter of the support structure 20 (including the electrodeelements 28, flexible sleeve 32, and the spline leg 22) can vary fromabout 2 French to about 10 French.

[0137] The support structure 20 must make and maintain intimate contactbetween the electrode elements 28 and the endocardium. Furthermore, thesupport structure 20 must be capable of assuming a relatively lowprofile for steering and introduction into the body.

[0138] To accomplish these objectives, the probe 10 includes a sheath 26carried by the catheter tube 12. The distal section 30 of the sheath 26extends about the multiple electrode structure 20 (see FIGS. 1 and 2A).The distal section 30 of the sheath 26 is joined to the end of themultiple electrode structure, e.g. by adhesive or thermal bonding.

[0139] In the embodiment shown in FIG. 1, the proximal section 34 of thesheath 26 terminates short of the handle 18 and includes a raisedgripping surface 36. The proximal section 34 also includes a hemostaticvalve and side port (not shown) for fluid infusion. Preferably thehemostatic valve locks about the catheter tube 12.

[0140] The distal section 30 of the sheath 26 (proximal of itsconnection to the multiple electrode structure 20) includes a preformedslot 40, which extends along the axis of the catheter tube 12 (see FIG.2A). A portion of the multiple electrode structure 20 is exposed throughthe slot 40.

[0141] The length and size of the slot 40 can vary, as will be describedin greater detail later. The circumferential distance that slot 40extends about the axis 42 can also vary, but is always less than theouter diameter of the sheath 26. Thus, a remnant 44 of the sheath 26underlies the slot 40. In the illustrated embodiment, the slot 40extends about 180° about the sheath 26.

[0142] The catheter tube 12 is slidable within the sheath in a forwardand rearward direction, as indicated by arrows 46 and 48 in FIG. 1. Bygrasping the raised gripping surface 36 at the proximal end of thesheath 26, and pushing the catheter tube 12 in the forward direction(arrow 46) through the sheath 26 (see FIG. 3A), the structure 20,secured to the catheter tube 12 and to the end 30 of the sheath 26,bends outwardly from the slot 40. The sheath remnant 44 forms a flexiblejoint, keeping the distal end of the structure 20 close to the cathetertube axis 42, while the element 20 bends into a loop, as FIG. 3A shows.The flexible joint 44 maintains loop stress within the structure 20, tothereby establish and maintain intimate contact between the electrodeelements 28 and tissue.

[0143] The physician can alter the diameter of the loop structure 20from large to small, by incrementally moving the catheter tube 12 in theforward and rearward directions (arrows 46 and 48) through the sheath26. In this way, the physician can manipulate the loop structure 20 toachieve the desired degree of contact between tissue and the electrodeelements 28.

[0144] If desired, the physician can, while grasping the raised grippingsurface 36, rotate the catheter tube 12 within the sheath 26. As FIG. 4Ashows, when the catheter tube 12 is torsionally stiffer than the sheath26, the relative rotation (arrow 50) flips the loop structure 20 overupon itself (compare FIGS. 3A and 4A), to place the electrode elements28 in a different orientation for tissue contact. As FIG. 4B shows, whenthe sheath 26 is torsionally stiffer than the catheter tube 12, rotationof the catheter tube within the sheath 26 bends the structure 20generally orthogonally to the axis of the loop.

[0145] By grasping the raised gripping surface 36 and pulling thecatheter tube 12 in the rearward direction (arrow 48), the physiciandraws the multiple electrode structure 20 back into the sheath 26, asFIG. 2A shows. Housed within the sheath 26, the multiple electrodestructure 20 and sheath 26 form a generally straight, low profilegeometry for introduction into and out of a targeted body region.

[0146] The sheath 26 is made from a material having a greater inherentstiffness (i.e., greater durometer) than the support structure 20itself. Preferably, the sheath material is relatively thin (e.g., with awall thickness of about 0.005 inch) so as not to significantly increasethe overall diameter of the distal region of the probe 10 itself. Theselected material for the sheath 26 is preferably also lubricious, toreduce friction during relative movement of the catheter tube 12 withinthe sheath 26. For example, materials made from polytetrafluoroethylene(PTFE) can be used for the sheath 26.

[0147] Additional stiffness can be imparted by lining the sheath 26 witha braided material coated with PEBAX™ material (comprising polyurethaneand nylon). Increasing the sheath stiffness imparts a more pronouncedD-shape geometry to the formed loop structure 20 orthogonal to the axisof the slot 40. Other compositions made from PTFE braided with a stiffouter layer and other lubricious materials can be used. Steps are takento keep remnants of braided materials away from the exposed edges of theslot 40. For example, the pattern of braid can be straightened to runessentially parallel to the axis of the sheath 26 in the region of theslot 40, so that cutting the slot does not cut across the pattern of thebraid.

[0148] The flexible joint 44 is durable and helps to shape the loopstructure. The flexible joint 44 also provides an anchor point for thedistal end 16 of the catheter tube 12. The joint 44 also providesrelatively large surface area, to minimize tissue trauma. The geometryof the loop structure 20 can be altered by varying either the stiffnessor the length of the flexible joint 44, or both at the same time.

[0149] As FIG. 3A shows, a stiffening element 52 can be placed along thejoint 44. For example, the stiffening element 52 can comprise anincreased durometer material (e.g., from about 35 D to about 72 D),which is thermally or chemically bonded to the interior of the joint 44.Examples of increased durometer materials, which will increase jointstiffness, include nylon, tubing materials having metal or nonmetallicbraid in the wall, and PEBAX™ material. Alternatively, the stiffeningelement 52 can comprise memory wire bonded to the interior of the joint44. The memory wire can possess variable thickness, increasing in theproximal direction, to impart variable stiffness to the joint 44,likewise increasing stiffness in the proximal direction. The memory wirecan also be preformed with resilient memory, to normally bias the joint44 in a direction at an angle to the axis of the slot 40.

[0150] As FIG. 3B shows, the stiffening element 52 can comprise one ormore lumens 546 within the joint 44, which carry wire material 548. Thelumens 546 and wire material 548 can extend only in the region of thejoint 44, or extend further in a proximal direction into the main bodyof the sheath 26, to thereby impart greater stiffness to the sheath 26as well.

[0151] As FIG. 3C shows, greater stiffness for the joint 44 can beimparted by extruding the sheath 26 to possess an eccentric wallthickness. In this arrangement, the wall of the sheath 26 has a region550 of greater thickness in the underbody of the sheath 26, whichbecomes the joint 44, than the region 552 which is cut away to form theslot 40. As shown in phantom lines in FIG. 3C, one or more of the lumens546 can be extruded in the thicker region 550, to receive wire materialto further stiffen the region of the joint 44.

[0152] Regardless of its particular form, the stiffening element 52 forthe joint 44 changes the geometry of the formed loop structure 20.

[0153] The geometry of the formed loop structure 20 can also be modifiedby altering the shape and size of the slot 40. The slot periphery canhave different geometries, e.g., rectangular (see FIG. 7A), elliptical(see FIG. 7B), or tapered (see FIG. 7C), to establish differentgeometries and loop stresses in the formed structure 20.

[0154] The effective axial length of the slot 44 can be adjusted by useof a movable mandrel 54, controlled by a push-pull stylet member 56 (seeFIG. 5) attached to a slider controller 58 in the handle 18. Axialmovement of the mandrel 54 affected by the stylet member 56 enlarges ordecreases the effective axial length of the slot 44. A nominal slotlength in the range of 1-¼ inch to 1-½ inch will provide the D-shapeloop structure 20 shown in FIG. 3A. Shorter slot lengths will provide aless pronounced D-shape, with a smaller radius of curvature. Larger slotlengths will provide a more pronounced D-shape, with a larger radius ofcurvature. As FIG. 8 shows, the proximal edge 60 of the slot 40 can betapered distally to guide bending of the structure 20 into the desiredloop shape while being advanced through the slot 40.

[0155] Instead of extending generally parallel to the catheter tube axis42, as FIGS. 1 to 8 show, the slot 40 can extend across the cathetertube axis 42, as FIG. 9 shows. When advanced from the cross-axis slot40, the loop structure 20 extends more orthogonally to the catheter tubeaxis 42, as FIG. 10 shows, compared to the more distal extensionachieved when the slot 40 is axially aligned with the catheter tube axis42, as FIG. 3A generally shows.

[0156] As FIG. 6 shows, a region 62 of the spline 22 within thestructure 20 away from the electrode elements 28 can be preformed withelastic memory to bow radially away from the electrode elements 28 whenadvanced from the sheath 26. The radially outward bow of the preformedregion 62 forms a more symmetric loop structure 20′, in contrast to themore asymmetric D-shaped loop 20 shown in FIG. 3A. When in contact withtissue, the preformed, outwardly bowed region 62 generates a backpressure that, in combination with the loop stress maintained by theflexible joint 44, establishes greater contact pressure betweenelectrode elements 28 and tissue.

[0157] In FIG. 6, the region 62 is preformed with a generally uniformbend in a single plane. The region 62 can be preformed with complex,serpentine bends along a single plane, or with bends that extend inmultiple planes. Further details of representative loop structureshaving complex, curvilinear geometries will be described in greaterdetail later.

[0158] Additional tissue contact forces can be generated by mounting abendable spring 64 in the distal end 16 of the catheter tube (see FIG.2A). One or more steering wires 66 are bonded (e.g., soldered, spotwelded, etc.) to the bendable spring 64 extend back to a steeringmechanism 68 in the handle 18 (see FIG. 1). Details of steeringmechanisms that can be used for this purpose are shown in Lundquist andThompson U.S. Pat. No. 5,254,088, which is incorporated into thisSpecification by reference. Operation of the steering mechanism 68 pullson the steering wires 66 to apply bending forces to the spring 64.Bending of the spring 64 bends the distal end 16 of the catheter tube12, as shown in phantom lines in FIG. 1.

[0159] The plane of bending depends upon the cross section of the spring64 and the attachment points of the wires 66. If the spring 64 isgenerally cylindrical in cross section, bending in different planes ispossible. If the spring 64 is generally rectilinear in cross section,anisotropic bending occurs perpendicular to the top and bottom surfacesof the spring 64, but not perpendicular to the side surfaces of thespring 64.

[0160] Alternatively, or in combination with the manually bendablespring 64, the distal end 16 of the catheter tube 12 can be prebent toform an elbow 70 (see FIG. 11) generally orthogonal or at some otherselected angle to the loop structure 20. In the illustrated embodiment,a preformed wire 72 is secured, e.g., by soldering, spot welding, orwith adhesive, to the end 16 of the catheter tube 12. The preformed wire72 is biased to normally curve. The preformed wire 72 may be made fromstainless steel 17/7, nickel titanium, or other memory elastic material.It may be configured as a wire or as a tube with circular, elliptical,or other cross-sectional geometry.

[0161] The wire 72 normally imparts its curve to the distal cathetertube end 16, thereby normally bending the end 16 in the direction of thecurve. The direction of the normal bend can vary, according to thefunctional characteristics desired. In this arrangement, a sheath 74slides (arrows 76) along the exterior of the catheter body 14 between aforward position overlying the wire 72 (FIG. 12) and an aft positionaway from the wire 72 (FIG. 11). In its forward position, the sheath 74retains the distal catheter end 16 in a straightened configurationagainst the normal bias of the wire 72, as FIG. 12 shows. The sheath 74may include spirally or helically wound fibers to provide enhancedtorsional stiffness to the sheath 74. Upon movement of the sheath 74 toits aft position, as FIG. 11 shows, the distal catheter end 16 yields tothe wire 72 and assumes its normally biased bent position. The slidablesheath 74 carries a suitable gripping surface (not shown), like thegripping surface 36 of the sheath 26, to affect forward and aft movementof the sheath 74 for the purposes described.

[0162]FIG. 4 shows the loop structure 20 flipped upon itself by rotationof the loop structure 20 within the sheath 26. The rotation is allowed,because both the loop structure 20 and sheath 26 possess generallycylindrical cross sections. If it is desired to prevent relativerotation of the structure 20 within the sheath 26, the outer geometry ofthe structure 20 and the interior geometry of the sheath 26 can beformed as an ellipse, as FIG. 13A shows. The interference (ellipticallykeyed) arrangement in FIG. 13A prevents rotation of the structure 20 andalso provides improved torque response and maintains the electrodeelements 28 is a fixed orientation with respect to the sheath 26. Bymatching the outer geometry of the structure 20 and the interiorgeometry of the sheath 26 (see FIG. 13B), a prescribed range of relativerotation can be allowed before interference occurs. In FIG. 13B, theelliptical sleeve 32 will rotate until it contacts the butterfly shapedkeyway within the sheath 26. The prescribed range allows the loopstructure 20 to be flipped over upon itself in the manner shown in FIG.4, without wrapping the flexible joint 44 about the sheath 26. Shouldthe flexible joint 44 become wrapped about the sheath 26, the physicianmust rotate of the catheter tube 12 to unwrap the joint 44, beforeretracting the structure 20 back into the slotted sheath 26.

[0163] B. Distal Wire Joint

[0164]FIGS. 14 and 15 show another structure 100 carrying multipleelectrode elements 28. In many respects, the structure 100 sharesstructural elements common to the structure 20 shown in FIGS. 2 and 3,as just discussed. For this reason, common reference numerals areassigned. Like the structure 20 shown in FIGS. 2 and 3, the structure100 is intended, in use, to be carried at the distal end 16 of aflexible catheter tube 12, as a part of a probe 10, as shown in FIG. 1.

[0165] Like the structure 20 shown in the FIGS. 2 and 3, the supportstructure 100 comprises a flexible spline leg 22 surrounded by aflexible, electrically nonconductive sleeve 32. The multiple electrodes28 are carried by the sleeve 32. The range of materials usable for thespline leg 22 and the electrodes 28 of the structure 100 are aspreviously described for the structure 20.

[0166] A sheath 102 is carried by the catheter tube 12. The distalsection 104 of the sheath 102 extends about the multiple electrodestructure 100. As FIGS. 14 and 15A show, the distal section 104 of thesheath 102 is joined to the distal end 108 of the multiple electrodestructure 100 by a short length of wire 106. The wire 106 is joined tothe two ends 104 and 108, for example, by adhesive or thermal bonding.The proximal section of the sheath 102 is not shown in FIG. 13, butterminates short of the handle 18 and includes a raised gripping surface36, as shown for the probe 10 in FIG. 1. In FIG. 15A, the wire 106 isjoined to the interior of the sheath 102. Alternatively, as FIG. 15Bshows, the wire 106 can be joined to the exterior of the sheath 102.

[0167] Like the sheath 26 described in connection with FIGS. 2 and 3A,the sheath 102 is made from a material having a greater inherentstiffness than the support structure 100 itself, e.g., compositematerials made from PTFE, braid, and polyimide. The selected materialfor the sheath 102 is preferably also lubricious. For example, materialsmade from polytetrafluoroethylene (PTFE) can be used for the sheath 102.As for the sheath 26 in FIGS. 2 and 3, additional stiffness can beimparted by incorporating a braided material coated with PEBAX™material.

[0168] The wire 106 comprises a flexible, inert cable constructed fromstrands of metal wire material, like Nickel Titanium or 17-7 stainlesssteel. Alternatively, the wire 106 can comprise a flexible, inertstranded or molded plastic material. The wire 106 in FIG. 14 is shown tobe round in cross section, although other cross sectional configurationscan be used. The wire 106 may be attached to the sheath 102 by thermalor chemical bonding, or be a continuation of the spline leg 22 thatforms the core of the structure 100. The wire 106 can also extendthrough the wall of the sheath 102, in the same way that the stiffeningwires 548 are placed within the sheath 26 (shown in FIG. 3B). The needto provide an additional distal hub component to secure the wire 106 tothe remainder of the structure 100, is thereby eliminated.

[0169] The catheter tube 12 is slidable within the sheath 102 to deploythe structure 100. Grasping the raised gripping surface 36 at theproximal end of the sheath 102, while pushing the catheter tube 12 inthe forward direction through the sheath 102 (as shown by arrow 110 inFIG. 15A), moves the structure 100 outward from the open distal end 112of the sheath 102. The wire 106 forms a flexible joint 144, pulling thedistal end 108 of the structure 100 toward the sheath distal section104. The structure 100 thereby is bent into a loop, as FIG. 15A shows.

[0170] The flexible wire joint 106, like the sheath joint 44 in FIG. 3A,possesses the flexibility and strength to maintain loop stress withinthe structure 100 during manipulation, to thereby establish and maintainintimate contact between the electrode elements 28 and tissue. The wire106 presents a relatively short length, thereby minimizing tissuetrauma. A representative length for the wire 106 is about 0.5 inch.

[0171] Like the loop structure 20, the physician can alter the diameterof the loop structure 100 from large to small, by incrementally movingthe catheter tube 12 in the forward direction (arrow 110 in FIG. 15) andrearward direction (arrow 116 in FIG. 15) through the sheath 102. Inthis way, the physician can manipulate the loop structure 100 to achievethe desired degree of contact between tissue and the electrode elements28.

[0172] Moving the structure 100 fully in the rearward direction (arrow116) returns the structure 100 into a low profile, generallystraightened configuration within the sheath 102 (as FIG. 14 shows),well suited for introduction into the intended body region.

[0173] The points of attachment of the wire joint 106 (between thedistal structure end 108 and the distal sheath section 104), coupledwith its flexible strength, make it possible to form loops with smallerradii of curvature than with the flexible sheath joint 44 shown in FIG.3A.

[0174] The geometry of the loop structure 100 can be altered by varyingeither the stiffness or the length of the flexible wire 106, or both atthe same time. As FIG. 16A shows, the flexible wire 106 can be tapered,to provide a cross section that decreases in the distal direction. Thetapered cross section provides varying stiffness, which is greatest nextto the sheath 102 and decreases with proximity to the distal end 108 ofthe structure 100.

[0175] The stiffness can also be changed by changing the thickness ofthe wire 106 in a step fashion. FIG. 16B shows the wire 106 attached tothe sheath 102 and having the smallest thickness to increase the bendingradius. The thickness of the wire 106 increases in a step fashionleading up to its junction with the spline leg 22. Changing thethickness of the wire can be done by rolling the wire in steps, or bypressing it, or by chemical etching.

[0176] As FIG. 16C shows, the wire 106 can also be used to impartgreater stiffness to the flexible joint 144, for the reasons describedearlier with regard to the flexible joint 44 shown in FIG. 3A. In FIG.16C, the wire 106 is thermally or chemically bonded to the flexiblejoint 144 in a serpentine path of increasing width. The alternative waysof stiffening the flexible joint 44 (shown in FIGS. 3A, 3B, and 3C) canalso be used to stiffen the flexible joint 144.

[0177] In the illustrated embodiment (see FIGS. 15A and 16A), the distalsheath section 104 is cut at an angle and tapered in a transversedirection relative to the axis of the sheath 102. The angled linear cuton the distal sheath section 104 may also be a contoured elongatedopening (see FIG. 15B) to make the initiation of the loop formationeasier. The angle cut on the sheath 102 helps deploy and minimizes thelength of the wire 106. It is advantageous to cover with the sheathsection 104 a significant portion of the wire joint 144. The sheathsection 104 thereby also serves to shield the wire as much as possiblefrom direct surface contact with tissue. The possibility of cuttingtissue due to contact with the wire 106 is thereby minimized.

[0178] As before described in the context of the structure 20,additional tissue contact forces between the structure 100 and tissuecan be generated by mounting a bendable spring 64 in the distal end 16of the catheter tube (see FIG. 14). Alternatively, or in combinationwith the manually bendable spring 64, the distal end 16 of the cathetertube 12 can be prebent to form an elbow 70 (as shown in FIG. 11 inassociation with the structure 20) generally orthogonal or at some otherselected angle to the loop structure 100.

[0179]FIG. 17A shows an alternative embodiment for the structure 100. Inthis embodiment, the wire 106 is not attached to the distal sheathsection 104. Instead, the wire 106 extends through the sheath 102 to astop 118 located proximal to the gripping surface 36 of the sheath 102.Holding the stop 118 stationary, the physician deploys the loopstructure 100 in the manner already described, by advancing the cathetertube 12 through the sheath 102 (arrow 120 in FIG. 17A). Once the loopstructure 100 has been formed, the physician can pull on the wire 106(arrow 122 in FIG. 17A) to decrease its exposed length beyond the distalsheath section 104, to minimize tissue trauma. Further adjustments tothe loop are made by advancing or retracting the catheter tube 12 withinthe sheath 102. The wire 106 unattached to the sheath 102 allows thephysician to interchangeably use the structure 100 with any sheath.

[0180] Alternatively, as FIG. 17B shows, the sheath 102 can include alumen 107 through which the wire 106 passes. In this embodiment, thepresence of the wire 106 within the body of the sheath 102 providesincreased torque. Unlike FIG. 17A, however, the sheath and the wire 106comprise one integrated unit and cannot be interchanged.

[0181] The embodiment shown in schematic form in FIGS. 18, 19, and 20offers additional options for adjusting the nature and extent of contactbetween the electrode elements 28 and tissue. As FIG. 18 shows, aflexible spline leg 124 extends from an external push-pull control 126through the catheter tube 12 and is looped back to a point of attachment128 within the catheter tube 12. A sheath 130, made of an electricallyinsulating material, is slidable along the spline leg 124, both withinand outside the catheter tube 12. The sheath 130 carries the electrodeelements 28. The proximal end of the sheath 130 is attached to a pushpull control 132 exposed outside the catheter tube 12.

[0182] By pushing both controls 126 and 132 simultaneously (arrows 134in FIG. 19), both the spline leg 124 and the sheath 130 are deployedbeyond the distal end 16 of the catheter tube 12. Together, the splineleg and sheath 130 form a loop structure 136 to present the electrodeelements 28 for contact with tissue, in much the same way that thestructure 100 and the structure 20, previously described, establishcontact between the electrode elements 28 and tissue.

[0183] In addition, by holding the spline leg control 126 stationarywhile pushing or pulling the sheath control 132 (arrows 134 and 136 inFIG. 20), the physician is able to slide the sheath 130, and thus theelectrode elements 28 themselves, along the spline leg 124 (as arrows138 and 140 in FIG. 20 show). The physician is thereby able toadjustably locate the region and extent of contact between tissue andthe electrode elements 28.

[0184] Furthermore, by holding the sheath control 132 stationary whilepushing or pulling upon the spline leg control 126, the physician isable to adjust the length of the spline leg 124 exposed beyond thedistal end 16 of the catheter tube 12. The physician is thereby able toincrementally adjust the radius of curvature in generally the samefashion previously described in the context of FIG. 17.

[0185] The arrangement in FIGS. 18, 19, and 20, thereby provides a widerange of adjustment options for establishing the desired degree ofcontact between tissue and the electrode elements 28 carried by the loopstructure 136.

[0186] By pulling both controls 126 and 128 simultaneously (arrows 142in FIG. 18), both the spline leg 124 and the sheath 130 are moved to aposition close to or within the distal end 16 of the catheter tube 12for introduction into a body region.

[0187] C. Free Pull Wire

[0188]FIG. 21 shows a multiple electrode support structure 144 formedfrom a spline leg 146 covered with an electrically insulating sleeve148. The electrode elements 28 are carried by the sleeve 148.

[0189] The structure 144 is carried at the distal end 16 of a cathetertube 12, and comprises the distal part of a probe 10, in the mannershown in FIG. 1. In this respect, the structure 144 is like thestructure 100, previously described, and the same materials aspreviously described can be used in making the structure 144.

[0190] Unlike the previously described structure100, a slidable sheath150 is intended to be moved along the catheter tube 12 and structure 144between a forward position, covering the structure 144 for introductioninto a body region (shown in FIG. 22), and an aft, retracted position,exposing the structure 144 for use (shown in FIGS. 21 and 23). Thus,unlike the structure 100, which is deployed by advancement forwardbeyond a stationary sheath 102, the structure 144 is deployed by beingheld stationary while the associated sheath 150 is moved rearward.

[0191] A pull wire 152 extends from the distal end 154 of the structure144. In the illustrated embodiment, the pull wire 152 is an extension ofthe spline leg 146, thereby eliminating the need for an additionaldistal hub component to join the wire 152 to the distal structure end154.

[0192] Unlike the structure 100, the pull wire 152 is not attached tothe sheath 150. Instead, the catheter tube 12 includes an interior lumen156, which accommodates sliding passage of the pull wire 152. The pullwire 152 passes through the lumen 156 to an accessible push-pull control166, e.g., mounted on a handle 18 as shown in FIG. 1. When the structure144 is free of the rearwardly withdrawn sheath 150, the physician pullsback on the wire 152 (arrow 168 in FIG. 23) to bend the structure 144into a loop.

[0193] As FIGS. 21 and 23 show, the wire 152 may include a preformedregion 158 adjacent to the distal structure end 154, wound into one ormore loops, forming a spring. The region 158 imparts a springcharacteristic to the wire 152 when bending the structure 144 into aloop. The region 158 mediates against extreme bending or buckling of thewire 152 during formation of the loop structure 144. The region 158thereby reduces the likelihood of fatigue failure arising after numerousflex cycles.

[0194]FIG. 24 shows an alternative embodiment for the structure 144. Inthis embodiment, the distal structure end 154 includes a slotted passage160, which extends across the distal structure end 154. In FIG. 24, theslotted passage 160 extends transverse of the main axis 162 of thestructure 144. Alternatively, the slottage passage 160 could extend atother angles relative to the main axis 162.

[0195] Unlike the embodiment shown in FIGS. 21 to 23, the wire 152 inFIG. 24 is not an extension of the spline leg 146 of the structure 144.Instead, the wire 152 comprises a separate element, which carries a ball164 at its distal end. The ball 164 is engaged for sliding movementwithin the slotted passage 160. The ball 164 also allows rotation of thewire 152 relative to the structure 144. The ball 164 and slotted passage160 form a sliding joint, which, like the spring region 158 in FIGS. 21to 23, reduces the likelihood of fatigue failure arising after numerousflex cycles.

[0196] As before described in the context of the structure 100,additional tissue contact forces between the structure 144 and tissuecan be generated by mounting a bendable spring 64 in the distal end 16of the catheter tube (see FIG. 21). Alternatively, or in combinationwith the manually bendable spring 64, the distal end 16 of the cathetertube 12 can be prebent to form an elbow (like elbow 70 shown in FIG. 11in association with the structure 20) generally orthogonal or at someother selected angle to the loop structure 144.

[0197] D. Preformed Loop Structures

[0198] 1. Single Loops

[0199]FIG. 25 shows an adjustable, preformed loop structure 170. Thestructure 170 is carried at the distal end 16 of a catheter tube 12,which is incorporated into a probe, as shown in FIG. 1.

[0200] The structure 170 includes a single, continuous, flexible splineelement 172 having two proximal ends 174 and 176. One proximal end 174is secured to the distal catheter tube end 16. The other proximal end176 slidably passes through a lumen 178 in the catheter tube 12. Theproximal end 176 is attached to an accessible push-pull control 180,e.g., mounted in the handle 18 shown in FIG. 1. The flexible splineelement 172 is bent into a loop structure, which extends beyond thedistal end 16 of the catheter tube 12. The spline element 172 can bepreformed in a normally bowed condition to accentuate the loop shape.

[0201] The continuous spline element 172 can be formed from resilient,inert wire, like Nickel Titanium or 17-7 stainless steel, or fromresilient injection molded inert plastic, or from composites. In theillustrated embodiment, the spline element 172 comprises a thin,rectilinear strip of resilient metal, plastic material, or composite.Still, other cross sectional configurations can be used.

[0202] As before described in connection with other structures, a sleeve182 made of, for example, a polymeric, electrically nonconductivematerial, like polyethylene or polyurethane or PEBAX™ material issecured, e.g., by heat shrinking, adhesives, or thermal bonding aboutthe spline element 172 in a region of the structure 170. The sleeve 182carries one or more electrode elements 28, which can be constructed inmanners previously described.

[0203] The structure 170 includes an interior wire 184. The interiorwire can be made from the same type of materials as the spline element172. The distal end of the wire 184 carries a cap 186, which is secured,e.g., by crimping or soldering or spot welding, to the wire 184. The capincludes a through passage 188 (see FIG. 26), through which the midportion of the spline element 172 extends. The spline element 172 isslidable within the through passage 188. It should be appreciated thatthe wire 184 can be attached to the spline element 172 in other ways topermit relative movement, e.g., by forming a loop or eyelet on thedistal end of the wire 184, through which the spline leg 172 passes. Itshould also be appreciated that the cap 186 can be secured to the splineleg 172, if relative movement is not desired.

[0204] The proximal end of the interior wire 184 slidably passes througha lumen 190 in the catheter tube 12 for attachment to an accessiblepush-pull control 192, e.g., also on a handle 18 like that shown in FIG.1.

[0205] As FIG. 27 shows, pushing on the control 180 (arrow 194) orpulling on the control 180 (arrow 196) moves the spline element 172 toalter the shape and loop stresses of the structure 170. Likewise,pushing on the control 192 (arrow 198) or pulling on the control 192(arrow 200) moves the interior wire 184 in the lumen 190, which appliesforce to the cap 186 in the midportion of the structure 172, and whichfurther alters the shape and loop stresses of the structure 170.

[0206] In particular, manipulation of the controls 180 and 192 createsasymmetric geometries for the structure 170, so that the physician isable to shape the structure 170 to best conform to the interior contoursof the body region targeted for contact with the electrode elements.Manipulation of the controls 180 and 192 also changes the backpressures, which urge the electrode elements 28 into more intimatecontact with tissue.

[0207] As FIG. 28 shows, further variations in the shape of and physicalforces within the structure 170 can be accomplished by bending theinterior wire 184 along its axis. In one embodiment, the wire 184 ismade from temperature memory wire, which bends into a preestablishedshape in response to exposure to blood (body) temperature, and whichstraightens in response to exposure to room temperature. Bending theinterior wire 184 imparts forces (through the cap 186) to bend thespline element 172 into, for example, an orthogonal orientation. Thisorientation may be required in certain circumstances to better accessthe body region where the electrode elements 28 are to be located incontact with tissue.

[0208] Alternatively, one or more steering wires (not shown) can beattached to the interior wire 184. Coupled to an accessible control (notshown), e.g. on the handle 18, pulling on the steering wires bends thewire 184, in generally the same fashion that the steering wires 66affect bending of the spring 64, as previously described with referenceto FIG. 2A.

[0209] As FIG. 29 shows, the control 192 can also be rotated (arrows222) to twist the interior wire 184 about its axis. Twisting the wire184 imparts (through the cap 186) transverse bending forces along thespline element 172. The transverse bending forces form curvilinear bendsalong the spline element 172, and therefore along the electrode elements28 as well. The loop stresses can also be further adjusted by causingthe control 180 to rotate (arrows 224) the spline element 172.

[0210] As FIG. 30 shows, the through passage cap 186 (see FIG. 26)permits the cap 186 to be repositioned along the spline element 172. Inthis way, the point where the wire 184 applies forces (either push-pull,or twisting, or bending, or a combination thereof) can be adjusted toprovide a diverse variety of shapes (shown in phantom lines) for andloop stresses within the structure 170. FIG. 31 shows, by way ofexample, how changing the position of the cap 186 away from themidregion of the spline element 172 alters the orthogonal bend geometryof the spline element 172, compared to the bend geometry shown in FIG.28. The cap 186 can be moved along the spline element 172, for example,by connecting steering wires 566 and 568 to the distal region of theinterior wire 184 Pulling on a steering wire 566 or 568 will bend theinterior wire 184 and slide the cap 186 along the spline element 172.

[0211] The single loop structure 170 is introduced into the targetedbody region within an advanceable sheath 218, which is slidably carriedabout the catheter tube 12 (see FIG. 25). Movement of the sheath 218forward (arrow 226 in FIG. 25) encloses and collapses the loop structure170 within the sheath 218 (in generally the same fashion that thestructure 144 in FIG. 21 is enclosed within the associated sheath 150).Movement of the sheath 218 rearward (arrow 230 in FIG. 25) frees theloop structure 170 of the sheath 218.

[0212] 2. Multiple Loop Assemblies

[0213] As FIG. 32 shows, the structure 170 can include one or moreauxiliary spline elements 202 in regions of the structure 170 spacedaway from the electrode elements 28. In the illustrated embodiment, theauxiliary spline elements 202 slidably extend through the distal cap 186as before described, and are also coupled to accessible controls 204 inthe manner just described. In this way, the shape and loop stresses ofthe auxiliary spline elements 202 can be adjusted in concert with thespline element 172, to create further back pressures to urge theelectrode 28 toward intimate contact with tissue. The existence of oneor more auxiliary spline elements 202 in multiple planes also make itpossible to press against and expand a body cavity, as well as providelateral stability for the structure 170.

[0214] As FIG. 33 shows, asymmetric mechanical properties can also beimparted to the structure 170, to improve contact between tissue and theelectrode elements 28. In FIG. 33 the region of the structure 170 whichcarries the electrode elements 28 is stiffened by the presence of theclosely spaced multiple spline elements 206A, 206B, and 206C. Spacedapart, single spline elements 208 provide a back-support region 210 ofthe structure 170.

[0215]FIG. 34 shows a multiple independent loop structure 220. Thestructure 220 includes two or more independent spline elements (threespline elements 212, 214, and 216 are shown), which are not commonlyjoined by a distal cap. The spline elements 212, 214, and 216 formindependent, nested loops, which extend beyond the distal end 16 of thecatheter tube 12.

[0216] A region 211 on each spline element 212, 214, and 216 carries theelectrode elements 28. The other region 213 of each spline element 212,214, and 216 is slidable within the catheter tube 12, being fitted withaccessible controls 212C, 214C, and 216C, in the manner just described.Thus, independent adjustment of the shape and loop stresses in eachspline element 212, 214, and 216 can be made to achieve desired contactbetween tissue and the electrode elements 28.

[0217] Like the single loop structures shown in FIGS. 25 to 31 thevarious multiple loop structures shown in FIGS. 32 to 34 can beintroduced into the targeted body region in a collapsed condition withina sheath 232 (see FIG. 32), which is slidably carried about the cathetertube 12. As FIG. 32 shows, movement of the sheath 232 away from the loopstructure frees the loop structure for use.

[0218] E. Orthogonal Loop Structures

[0219]FIGS. 28 and 31 show embodiments of loop structures 170, whichhave been bent orthogonally to the main axis of the structure 170. Inthese embodiments the orthogonal bending is in response to bending aninterior wire 184.

[0220]FIGS. 35 and 36 show a loop structure 232 that assumes anorthogonal geometry (in FIG. 36) without requiring an interior wire 184.The structure 232, like the structure 170 shown in FIG. 25, is carriedat the distal end 16 of a catheter tube 12, which is incorporated into aprobe, as shown in FIG. 1.

[0221] Like the structure 170, the structure 232 comprises a single,continuous, flexible spline element 234. One proximal end 236 is securedto the distal catheter tube end 16. The other proximal end 238 passesthrough a lumen 240 in the catheter tube 12. The proximal end 238 isattached to an accessible control 242, e.g., mounted in the handle 18shown in FIG. 1. As in the structure 170, the spline element 234 can bepreformed in a normally bowed condition to achieve a desired loopgeometry.

[0222] In FIGS. 35 and 36 the spline element 234 is formed, e.g., frominert wire, like Nickel Titanium or 17-7 stainless steel, or fromresilient injection molded inert plastic, with two regions 244 and 246having different cross section geometries. The region 244, whichcomprises the exposed part of the spline element 234 that carries theelectrode elements 28, possesses a generally rectilinear, or flattenedcross sectional geometry, as FIG. 37 shows. The region 246, whichcomprises the part of the spline element 234 extending within thecatheter tube 12 and attached to the control 240, possesses a generallyround cross sectional geometry, as FIG. 38 shows. To provide the tworegions 244 and 246, a single length of round wire can be flattened andannealed at one end to form the rectilinear region 244.

[0223] Rotation of the control 242 (attached to the round region 246)(arrows 250 in FIG. 35) twists the rectilinear region 244 about theproximal end 236, which being fixed to the catheter tube 12, remainsstationary. The twisting rectilinear region 244 will reach a transitionposition, in which the region 244 is twisted generally 90° from itsoriginal position (as FIG. 39 shows). In the transition position, theloop structure 232 bends orthogonal to its main axis, as FIG. 36 shows.By stopping rotation of the control 242 once the transition position isreached, the retained twist forces in the loop structure 232 hold theloop structure 232 in the orthogonally bent geometry.

[0224]FIGS. 42A and 42B show an alternative embodiment, in which eachleg 554 and 556 of a loop structure 558 is attached to its ownindividual control, respectively 560 and 562. The region 564 of the loopstructure 558 carrying the electrode element 28 possesses a generallyrectilinear or flattened cross section. The regions of the legs 554 and556 near the controls 560 and 562 possess generally round crosssections. Counter rotation of the controls 560 and 562 (respectivelyarrows 561 and 563 in FIG. 42B), twists the rectilinear region 564 tobend the loop structure 558 generally orthogonal to its axis (as FIG.42B shows). The counter rotation of the controls 560 and 562 can beaccomplished individually or with the inclusion of a gear mechanism.

[0225] In both embodiments shown in FIGS. 36 and 42B once the orthogonalbend is formed and placed into contact with tissue, controlleduntwisting of the spline legs will begin to straighten the orthogonalbend in the direction of tissue contact. Controlled untwisting canthereby be used as a counter force, to increase tissue contact.

[0226] The characteristics of the orthogonally bent geometry depend uponthe width and thickness of the rectilinear region 244. As the ratiobetween width and thickness in the region 244 increases, the morepronounced and stable the orthogonal deflection becomes.

[0227] The diameter of the loop structure 232 also affects thedeflection. The smaller the diameter, the more pronounced thedeflection. Increases in diameter dampen the deflection effect. Furtherincreases beyond a given maximum loop diameter cause the orthogonaldeflection effect to be lost.

[0228] The characteristics of the electrical insulation sleeve 248,which carries the electrode elements 28, also affect the deflection.Generally speaking, as the stiffness of the sleeve 248 increases, thedifficulty of twisting the region 244 into the transition positionincreases. If the sleeve 248 itself is formed with a non-round crosssection, e.g. elliptical, in the rectilinear region 244 the orthogonaldeflection characteristics are improved.

[0229] The orthogonal deflection effect that FIGS. 35 and 36 show canalso be incorporated into the loop structure of the type previouslyshown in FIG. 14. In this embodiment (see FIG. 40), the loop structure252 comprises a spline leg 254 (see FIG. 41 also) enclosed within anelectrically conductive sleeve 256, which carries the electrode elements28. The distal end of the structure 252 is attached by a joint wire 260to a sheath 258. As previously described, advancing the structure 252from the sheath 258 forms a loop (as FIG. 40 shows)

[0230] In the embodiment shown in FIG. 40 the spline leg 254 isrectilinear in cross section (see FIG. 41). Furthermore, as FIG. 41shows, the spline leg 254 is preformed in a normally twisted condition,having two sections 262 and 264. The section 262 is distal to thesection 264 and is attached to the joint wire 260. The sections 262 and264 are arranged essentially orthogonally relative to each other, beingoffset by about 90°. When advanced outside the sheath 258, the twistedbias of the rectilinear spline leg 254 causes the formed loop structure252 to bend orthogonally to its main axis, as FIG. 40 shows.

[0231] In an alternative embodiment (see FIG. 43), the structure 252 caninclude a spline leg 266 preformed to include along its length one ormore stressed elbows 268. The prestressed elbows 268 impart anorthogonal deflection when the structure 252 is free of the constraintof the sheath 270. When housed within the sheath 270, the stiffness ofthe sheath 270 straightens the elbows 268.

[0232] F. Deployment of Flexible Loop Structures

[0233] 1. Generally

[0234] Various access techniques can be used to introduce the previouslydescribed multiple electrode structures into a desired region of thebody. In the illustrated embodiment (see FIG. 44), the body region isthe heart, and the multiple electrode structure is generally designatedES.

[0235] During introduction, the structure ES is enclosed in astraightened condition within its associated outer sheath (generallydesignated S in FIG. 44 at the end 16 of the catheter tube 12. To enterthe right atrium of the heart, the physician directs the catheter tube12 through a conventional vascular introducer (designated with acapital-I in FIG. 44 into, e.g., the femoral vein. For entry into theleft atrium, the physician can direct the catheter tube 12 through aconventional vascular introducer retrograde through the aortic andmitral valves, or can use a transeptal approach from the right atrium.

[0236] Once the distal end 16 of the catheter tube 12 is located withinthe selected chamber, the physician deploys the structure ES in themanners previously described, i.e., either by advancing the structure ESforward through the sheath S (e.g., as in the case of the structuresshown in FIG. 3 or 15) or by pulling the sheath S rearward to expose thestructure ES (e.g., as in the case of the structures shown in FIG. 21 or25).

[0237] It should be appreciated that the structure ES discussed above inthe context of intracardiac use, can also be directly applied to theepicardium through conventional thoracotomy or thoracostomy techniques.

[0238] 2. Loop Structures

[0239] The various loop structures previously described (shown in FIGS.1 to 31, when deployed in the left or right atrium tend to expand theatrium to its largest diameter in a single plane. The loop structuretends to seek the largest diameter and occupy it. The loop structurescan also be adapted to be torqued, or rotated, into different planes,and thereby occupy smaller regions.

[0240] The addition of auxiliary splines, such as shown in FIGS. 32 to34 serves to expand the atrium in additional planes. The auxiliarysplines also make it possible to stabilize the structure against a morerigid anatomic structure, e.g. the mitral valve annulus in the leftatrium, while the spline carrying the electrode elements loops upwardtoward anatomic landmarks marking potential ablation sites, e.g., tissuesurrounding the pulmonary veins.

[0241] The various structures heretofore described, which exhibitcompound or orthogonal bends (see, e.g., FIGS. 28, 31, 35, 40, 42, and43 (which will be referred to as a group as “Compound Bend Assemblies”)also make it possible to locate the ablation and/or mapping electrode(s)at any location within a complex body cavity, like the heart. With priorconventional catheter designs, various awkward manipulation techniqueswere required to position the distal region, such as prolapsing thecatheter to form a loop within the atrium, or using anatomical barrierssuch as the atrial appendage or veins to support one end of the catheterwhile manipulating the other end, or torquing the catheter body. Whilethese techniques can still be used in association with the compound bendassemblies mentioned above, the compound bend assemblies significantlysimplify placing electrode(s) at the desired location and thereaftermaintaining intimate contact between the electrode(s) and the tissuesurface. The compound bend assemblies make it possible to obtain bettertissue contact and to access previously unobtainable sites, especiallywhen positioning multiple electrode arrays.

[0242] Compound bend assemblies which provide a proximal curved sectionorthogonal to the distal steering or loop geometry plane allow thephysician to access sites which are otherwise difficult and oftenimpossible to effectively access with conventional catheterconfigurations, even when using an anatomic barrier as a supportstructure. For example, to place electrodes between the tricuspidannulus and the cristae terminalis perpendicular to the inferior venacava and superior vena cava line, the distal tip of a conventional thecatheter must be lodged in the right ventricle while the catheter istorqued and looped to contact the anterior wall of the right atrium.Compound bend assemblies which can provide a proximal curved sectionorthogonal to the distal steering or loop geometry plane greatlysimplify positioning of electrodes in this orientation. Compound bendassemblies which provide a proximal curved section orthogonal to thedistal steering or loop geometry plane also maintain intimate contactwith tissue in this position, so that therapeutic lesions contiguous inthe subepicardial plane and extending the desired length, superiorlyand/or inferiorly oriented, can be accomplished to organize and helpcure atrial fibrillation.

[0243] A transeptal approach will most likely be used to create leftatrial lesions. In a transeptal approach, an introducing sheath isinserted into the right atrium through the use of a dilator. Once thedilator/sheath combination is placed near the fossa ovalis underfluoroscopic guidance, a needle is inserted through the dilator and isadvanced through the fossa ovalis. Once the needle has been confirmed toreside in the left atrium by fluoroscopic observation of radiopaquecontrast material injected through the needle lumen, the dilator/sheathcombination is advanced over the needle and into the left atrium. Atthis point, the dilator is removed leaving the sheath in the leftatrium.

[0244] A left atrial lesion proposed to help cure atrial fibrillationoriginates on the roof of the left atrium, bisects the pulmonary veinsleft to right and extends posteriorly to the mitral annulus. Since thelesion described above is perpendicular to the transeptal sheath axis, acatheter which can place the distal steering or loop geometry planeperpendicular to the sheath axis and parallel to the axis of the desiredlesion greatly enhances the ability to accurately place the ablationand/or mapping element(s) and ensures intimate tissue contact with theelement(s). To create such lesions using conventional catheters requiresa retrograde procedure. The catheter is advanced through the femoralartery and aorta, past the aortic valve, into the left ventricle, upthrough the mitral valve, and into the left atrium. This approachorients the catheter up through the mitral valve. The catheter must thenbe torqued to orient the steering or loop geometry plane parallel to thestated lesion and its distal region must be looped over the roof of theleft atrium to position the ablation and/or mapping element(s) bisectingthe left and right pulmonary veins and extending to the mitral annulus.

[0245] Preformed guiding sheaths have also been employed to changecatheter steering planes. However, preformed guiding sheaths have beenobserved to straighten in use, making the resulting angle different thanthe desired angle, depending on the stiffness of the catheter.Furthermore, a guiding sheath requires a larger puncture site for aseparate introducing sheath, if the guiding sheath is going to becontinuously inserted and removed. Additional transeptal puncturesincrease the likelihood for complications, such as pericardial effusionand tamponade.

[0246] G. Loop Size Marking

[0247]FIG. 87 shows a probe 524 comprising a catheter tube 526 carryinga slotted sheath 528 of the type previously described and shown, e.g.,in FIG. 1. The catheter tube 526 includes proximal handle 529 and adistal multiple electrode array 530. The multiple electrode array 530 isdeployed as a loop structure from the slotted sheath 528, in the mannerpreviously described and shown, e.g., in FIG. 3A.

[0248] In FIG. 87, the probe 524 includes indicia 532 providing thephysician feedback on the size of the formed loop structure. In FIG. 87,the indicia 532 comprises markings 534 on the region of the cathetertube 526 extending through the proximal end of the sheath 528. Themarkings 534 indicate how much of the catheter tube 526 has beenadvanced through the sheath 528, which thereby indicates the size of theformed loop structure.

[0249] The markings 534 can be made in various ways. They can, forexample, be placed on the catheter tube 526 by laser etching, or byprinting on the catheter tube 526 using bio-compatible ink, or by theattachment of one or more premarked, heat shrink bands about thecatheter tube 526.

[0250] In FIG. 88, the slotted sleeve 528 is attached to the handle 529of the probe 524. In this arrangement, the catheter tube 526 is advancedand retracted through the slotted sheath 528 by a push-pull control 536on the handle 529. In this embodiment, the indicia 532 providingfeedback as to the size of the formed loop structure includes markings536 on the handle 529, arranged along the path of travel of thepush-pull control 536. The markings 536 can be applied to the handle529, e.g., by laser etching ot printing. As in FIG. 87, the markings 536indicate how much of the catheter tube 526 has been advanced through theslotted sheath 528.

[0251] G. Movable Steering

[0252]FIG. 89 shows a movable steering assembly 570. The assembly 570includes a bendable wire 572 with at least one attached steering wire(two wires 574 and 576 are shown). The steering wires 574 and 576 areattached, e.g. by spot welding or soldering, to the bendable wire 572.The bendable wire 572 can be formed from resilient, inert wire, likeNickel Titanium or 17-7 stainless steel, or from resilient injectionmolded inert plastic, or from composites. In the illustrated embodiment,the wire 572 comprises a rectilinear strip of resilient metal, plasticmaterial, or composite. Still, other cross sectional configurations canbe used. The distal end 598 of the wire 572 is formed as a ball oranother blunt, nontraumatic shape.

[0253] The steering wires 574 and 576 are attached to an accessiblecontrol 584. The control 584 can take the form, for example, of arotatable cam wheel mechanism of the type shown in Lundquist andThompson U.S. Pat. No. 5,254,088, which is already incorporated intothis Specification by reference. Pulling on the steering wires 574 and576 (arrows 600 in FIG. 89), e.g., by rotating the control 584, bendsthe wire 572 in the direction of the pulling force.

[0254] The bendable wire 572 is attached by a ferrule 580 to a guidecoil 578. The guide coil 578 provides longitudinal support for thebendable wire 572. The guide coil 578 acts as the fulcrum about whichthe steering assembly 570 bends.

[0255] The assembly 570, comprising the bendable wire 572, steeringwires 574 and 576, and guide coil 578, is carried within an outerflexible tube 582. Operation of the control 584, to deflect the wire 572within the tube 582, bends the tube 582.

[0256] Taking into account the rectilinear shape of the bendable wire572, the outer tube 582 is ovalized. The interference between therectilinear exterior shape of the wire 572 and the oval interior shapeof the tube 582 prevents rotation of the wire 572 within the tube 582.The interference thereby retains a desired orientation of the bendablewire 572 with respect to the tube 582, and thus the orientation of theapplied bending forces.

[0257] The assembly 570 is attached to an accessible control 582.Pushing and pulling on the control 570 (arrows 602 and 604 in FIG. 89)axially moves the steering assembly 570 within the tube 582. Axialmovement of the assembly 570 changes the axial position of the bendablewire 572 within the tube 582. The control 570 thereby adjusts thelocation where bending forces are applied by the wire 572 along the axisof the tube 582.

[0258]FIGS. 90 and 91 show the movable steering assembly 570incorporated into a loop structure 586 of the type previously disclosedwith reference to FIG. 25, except there is no interior wire 184. Theloop structure 586 includes a spline 588 (see FIG. 91), which forms aloop. A sleeve 590 surrounds the spline 588. One or more electrodeelements 28 are carried by the sleeve 590.

[0259] As FIG. 91 shows, the sleeve 590 includes an ovalized interiorlumen 592, which carries the movable steering assembly 570. The steeringassembly 570, attached to the accessible control 582, is movable withinthe lumen 592 along the spline 588, in the manner just described withrespect to the ovalized tube 582 in FIG. 89.

[0260] As FIG. 92 shows, operating the control 584 to actuate thesteering wires 574 and 576 exerts a bending force (arrow 604) upon thespline 588 (through the bendable wire 572). The bending force alters theshape of the loop structure 586 in the plane of the loop, by increasingor decreasing its diameter. Shaping the loop structure 586 using thesteering mechanism 570 adjusts the nature and extent of tissue contact.

[0261] Because the steering mechanism 570 is movable, the physician canselectively adjust the location of the bending force (arrow 604) to takeinto account the contour of the tissue in the particular accessed bodyregion.

[0262] As FIG. 93 shows, the loop structure 586 can carry more than onemovable steering mechanism. In FIG. 93, there are two moveable steeringmechanisms, designated 570(1) and 570(2), one carried on each leg of thestructure 586. A separate steering control designated 584(1) and 584(2),and a separate axial movement control, designated 582(1) and 582(2) canalso be provided. It is therefore possible to independently adjust theposition of each steering mechanism 570(1) and 570(2) and individuallyapply different bending forces, designated, respectively, arrows 604(1)and 604(2). The application of individually adjustable bending forces(arrows 604(1) and 604(2)) allow diverse changes to be made to the shapeof the loop structure 586.

[0263] It should also be appreciated that the movable steering mechanism570 can be incorporated into other loop structures including those ofthe type shown in FIG. 33.

[0264] II. Self-Anchoring Multiple Electrode Structures

[0265] 1. Integrated Branched Structures

[0266]FIGS. 45 and 46 show an integrated branched structure 272, whichcomprises an operative branch 274 and an anchoring branch 276 orientedin an angular relationship. The branched structure 274 occupies thedistal end 16 of a catheter tube 12, and forms the distal part of aprobe 10, as shown in FIG. 1.

[0267] It should be appreciated that there may be more than oneoperative branch or more than one anchoring branch. The two branches 274and 276 are shown and described for the purpose of illustration.

[0268] The operative branch 274 carries one or more operative elements.The operative elements can take various forms. The operative elementscan be used, e.g., to sense physiological conditions in and near tissue,or to transmit energy pulses to tissue for diagnostic or therapeuticpurposes. As another example, the operative elements may take the formof one or more tissue imaging devices, such as ultrasound transducers oroptical fiber elements. By way of further example, the operativeelements can comprise biopsy forceps or similar devices, which, in use,handle tissue. The operative elements can also comprise optical fibersfor laser ablation, or a fluorescence spectroscopy device.

[0269] In the illustrated embodiment, the operative elements take theform of the electrode elements 28 (as previously described). In use, theelectrode elements 28 contact tissue to sense electrical events, or totransmit electrical pulses, e.g., to measure the impedance of or to paceheart tissue, or to transmit electrical energy to ablate tissue.

[0270] In the illustrated embodiment, the operative branch 274 comprisesa spline element 282 enclosed within an electrically insulating sleeve284. The spline element 282 can be formed, e.g., from resilient, inertwire, like Nickel Titanium or 17-7 stainless steel, or from resilientinjection molded inert plastic. In the illustrated embodiment, thespline element 282 comprises a thin, rectilinear strip of resilientmetal or plastic material. Still, other cross sectional configurationscan be used. Furthermore, more than a single spline element may be used.

[0271] As before described in the context of other structures, a sleeve282 made of, for example, a polymeric, electrically nonconductivematerial, like polyethylene or polyurethane or PEBAX™ material issecured about the spline element 282. The sleeve 282 carries theelectrode elements 28, which can also be constructed in mannerspreviously described.

[0272] In the illustrated embodiment, the operative branch 274 extendsat about a 45° angle from the anchoring branch 276. Various other anglesbetween 0° (i.e., parallel) and 90° (i.e., perpendicular) can be used.

[0273] The angular relationship between the operative branches 274 andthe anchoring branch 276 causes the operative branch 274 to inherentlyexert force against tissue as it is advanced toward it. The splineelement 282, or the sleeve 284, or both, can be stiffened to bias theoperative branch 274 toward the anchoring branch 276, to thereby enhancethe inherent tissue contact force.

[0274] As FIG. 46 best shows, the anchoring branch 276 comprises atubular body 286 defining an interior lumen 288, which extends throughthe catheter tube 12. The distal end 290 of the body 286 may be extendedoutward beyond the distal end 16 of the catheter tube 12, generallyalong the same axis 292 as the catheter tube 12. The proximal end 296 ofthe body 286 communicates with an accessible inlet 294, e.g., located onthe catheter tube 12 or on the handle 18.

[0275] The inlet 294 accommodates passage of a conventional guide wire306 into and through the lumen 288. The guide wire 306 includes a bluntdistal end 308 for nontraumatic contact with tissue.

[0276] As FIG. 47 shows, the body 286 can be carried within the cathetertube 12 for sliding movement forward (arrow 298) or rearward (arrow300). In this embodiment, an accessible control 302, e.g., located onthe handle 18, is coupled to the body 286 to guide the movement. In thisway, the physician can withdraw the body 286 within the catheter tube 12during introduction of the structure 272 into the body region. Thephysician can also adjust the relative length of the body 286 beyond thedistal end 16 of the catheter tube 16 to aid in positioning andanchoring the structure 272, once deployed within the targeted bodyregion.

[0277] An exterior sheath 304 is slidable along the catheter tube 12between a forward position (FIG. 48) and a rearward position (FIG. 45).In the forward position, the sheath 304 encloses and shields theoperative branch 274, straightening it. When in the forward position,the sheath 304 also encloses and shields the anchoring branch 274. Inthe rearward position, the sheath 304 frees both branches 274 and 276for use.

[0278] In use within the heart (see FIGS. 49A, 49B, and 49C), thephysician maneuvers the guide wire 306 through and outwardly of thelumen 288, with the aid of fluoroscopy or imaging, to a desired anchorsite. FIGS. 50A and 50B show candidate anchor sites within the heart,which surround anatomic structures that most commonly develop arrhythmiasubstrates, such as the superior vena cava SVC; right pulmonary veins(RPV); and left pulmonary veins (LPV); inferior vena cava (IVC); leftatrial appendage (LAA); right atrial appendage (RAA); tricuspid annulus(TA); mitral annulus (MA); and transeptal puncture (TP). The physicianpositions the blunt end portion 308 near tissue at the anchor site (seeFIG. 49A).

[0279] As FIG. 49B shows, the physician advances the structure 272,enclosed within the sheath 304, along the anchored guide wire 306. Whennear the anchor site, the physician retracts the sheath 304, freeing thestructure 272.

[0280] As FIG. 49C shows, the physician advances the anchoring branch276 along the guide wire 306 into the anchor site. The anchoring branch276 provides a support to place the operative branch 274 in contact withtissue in the vicinity of the anchor site.

[0281] Radiopaque makers 326 can be placed at preestablished positionson the structure 272 for visualization under fluoroscopy, to thereby aidin guiding the structure 272 to the proper location and orientation.

[0282]FIG. 55 shows an alternative embodiment of the anchoring branch276. In this embodiment, the anchoring branch 276 carries an inflatableballoon 346 on its distal end. The balloon 346 is inflated to secure theattachment of the anchoring branch 276 to the targeted vessel or cavityanchor site. The anchoring branch 276 includes a lumen 352 that extendsthrough the balloon 346, having an inlet 348 at the distal end of theballoon 346 and an outlet 350 at the proximal end of the balloon 346.The lumen 352 allows blood to flow through the targeted vessel or cavityanchor site, despite the presence of the anchoring balloon 346. Thelumen 306 also allows passage of the guide wire 306 for guiding theanchoring branch 276 into position.

[0283] As FIG. 46 shows, the operative branch 274 can carry one or moresteering wires 310 coupled to a bendable spring 312. Coupled to anaccessible control 314, e.g. on the handle 18, pulling on the steeringwires 310 bends the spring 312, in generally the same fashion that thesteering wires 66 affect bending of the spring 64, as previouslydescribed with reference to FIG. 2A. The physician is thereby able toaffirmatively bend the operative branch 274 relative to the anchoringbranch 276 to enhance site access and tissue contact. The steering wires310 can be coupled to the spring 312 to affect bending in one plane orin multiple planes, either parallel to the catheter axis 292 or notparallel to the axis 292.

[0284] Alternatively, or in combination with the manually bendablespring 312, the spline element 282 can be prebent to form an elbow (likeelbow 70 shown in FIG. 11 in association with the structure 20)generally orthogonal or at some other selected angle to the axis 292 ofthe catheter tube 12. The spline element 282 can also be prebent into acircular or elliptical configuration. For example, a circularconfiguration can be used to circumscribe the pulmonary veins in theleft atrium.

[0285] Alternatively, or in combination with a bendable operative branch274, the distal end 16 of the catheter tube 12 can include anindependent steering mechanism (see FIG. 49C, e.g., including a bendablewire 64 and steering wires 66, as previously described and as also shownin FIG. 2A. By steering the entire distal end 16, the physician orientsthe branched structure 272 at different angles relative to the targetedanchor site.

[0286] 2. Slotted Branch Structures

[0287]FIG. 51 shows an embodiment of a branched structure 272, in whichthe operative branch 274 can be moved in an outward direction (arrow316) and an inward direction (arrow 318) relative to the catheter tube12. In this embodiment, the operative branch 274 comprises a tubularbody 322, which slidably extends through a lumen 324 in the cathetertube 12. An accessible control 328 on the proximal end of the body 322guides the sliding movement.

[0288] The spline element 282, insulating sleeve 284, and operativeelements (i.e., electrode elements 28), already described, are carriedat the distal end of the slidable body 322. The catheter tube 12includes a slot 320 near the distal end 16, through which the slidablebody 322 passes during outward and inward movement 316 and 318.

[0289] The ability to move the operative branch 274 outside the cathetertube 12 enables the physician to define the number of electrodes 28contacting the tissue, and thereby define the length of the resultinglesion. Alternatively, a movable operative branch 274 allows thephysician to drag a selected activated electrode element 28 alongtissue, while the anchoring branch 276 provides a stationary point ofattachment.

[0290] The slidable body 322 can also be attached and arranged forrotation (arrows 352 in FIG. 51) with respect to the catheter tube 12,if desired, by making the exterior contour of the slidable body 322 andthe interior of the lumen 324 matching and symmetric. Rotation of theslidable body 322 can be prevented or restricted, if desired, byproviding an exterior contour for the slidable body 322 that isasymmetric, and sliding the body 322 through a matching asymmetricanchor or lumen within the slot 320 or within the catheter tube 12.

[0291] As FIG. 51 shows, radiopaque makers 326 are placed near the slot320 and near the distal tip of the operative element 274 forvisualization under fluoroscopy. The markers 326 can be located at otherparts of the structure 274, as well, to aid in manipulating theoperative branch 274 and anchoring branch 276.

[0292] The operative branch 274 shown in FIG. 51 can include a steeringspring and steering wires in the manner previously shown and describedin FIG. 46. All other mechanisms also previously described to bend theoperative branch 274 in planes parallel and not parallel to the catheteraxis 292 can also be incorporated in the FIG. 51 embodiment.

[0293]FIG. 52 shows an embodiment, like FIG. 51, except that thecatheter body 12 also carries an accessible control 330 to rotate theslot 320 about the catheter tube axis 292 (arrows 352 in FIG. 52). Ifthe operative branch 272 is free to rotated upon itself (as previouslydescribed), and if the spline element 282 within the operative branch274 is circular in cross section, the operative branch 274 will rotateupon itself during rotation of the slot 320. In this arrangement,rotation of the slot 320 torques the operative branch about the cathetertube axis 292.

[0294] On the other hand, if the spline element 282 within the operativebranch 274 is rectangular in cross section, the operative branch 274will rotate upon itself during rotation of the slot 320, provided thatrotation of the operative branch 274 about its axis is not prevented,and provided that the angle (a in FIG. 52) between the axis 332 of theoperative branch 274 and the axis 292 of the catheter tube 12 is lessthan 20°. Otherwise, an operative branch 274 with a rectilinear splineelement 282, will not rotate upon itself during rotation of the slot320, and thus can not be torqued by rotation of the slot 320.

[0295]FIG. 53 shows an embodiment of the structure 272, which like FIG.51, allows movement of the operative branch 274 through a slot 320.Unlike the embodiment in FIG. 51, the embodiment shown in FIG. 53includes a pull wire 334 attached to the distal end 336 of the operativebranch 274. The pull wire 334 passes through the exterior sheath 304 orthrough the catheter tube 12 (previously described) to an accessiblestop 336. Advancing the operative branch 274 forward (arrow 338) throughthe slot 320, while holding the pull wire 334 stationary, bends theoperative branch 274 into a loop, in much the same manner previouslydescribed in connection with the FIG. 15A embodiment. Pulling on thewire 334 (arrow 342) reduces the amount of exposed length beyond thedistal end of the sheath 304. By advancing the catheter tube (arrow340), the radius of curvature of the looped operative branch 274 can beadjusted, in much the same way previously shown in the FIG. 17Aembodiment.

[0296]FIG. 54 shows an embodiment of the structure 272, which like FIG.51, allows movement of the operative branch 274 through a slot 320.Unlike the embodiment in FIG. 51, the embodiment shown in FIG. 53includes a flexible joint 344 which joins the distal end 336 of theoperative branch 274 to the distal end 16 of the catheter tube 12.Advancing the operative branch 274 forward (arrow 338) through the slot320, bends the operative branch 274 into a loop, in much the same mannerpreviously described in connection with the FIGS. 3 and 15 embodiments.The flexible joint 344 can comprise a plastic material or a metalmaterial, as the preceding FIGS. 3 and 15 embodiments demonstrate.

[0297] 3. Spanning Branch Structures

[0298]FIG. 56 shows a self-anchoring multiple electrode structure 356comprising multiple operative branches (two operative branches 358 and360 are shown in FIG. 56). Like the operative branch 274 shown in FIG.45 each operative branch 358 and 360 carries one or more operativeelements, which can take various forms, and which in the illustratedembodiment comprise the electrode elements 28. Each operative branch 358and 360 likewise comprises a spline element 362 enclosed within anelectrically insulating sleeve 364, on which the electrode elements 28are carried.

[0299] In the illustrated embodiment, the operative branches 358 and 360are jointly carried within a catheter sheath 370. Each operative branch358 and 360 is individually slidable within the sheath 370 between adeployed position (FIG. 56) and a retracted position (FIG. 57). Itshould be appreciated that each operative branch 358 and 360 can bedeployed and retracted in an individual sheath.

[0300] Each operative element 358 and 360 includes a distal region,respectively 366 and 368, which are mutually bent outward in a“bow-legged” orientation, offset from the main axis 372 of the sheath370. This outwardly bowed, spaced apart relationship between the regions366 and 368 can be obtained by prestressing the spline elements 362 intothe desired shape, or by providing a spring which is actively steered bysteering wires (as described numerous times before), or both. Thedesired mutual orientation of the branches 358 and 360 can be retainedby making at least the proximal portion of the spline elements 362 notround, thereby preventing relative rotation of the branches 358 and 360within the sheath 370.

[0301] In use (see FIG. 58), each distal region 366 and 368 is intendedto be individually maneuvered into spaced apart anchoring sites, e.g.,the pulmonary veins (PV in FIG. 58). Once both regions 366 and 368 aresuitably anchored, the operative branches 360 and 362 are advanceddistally, toward the anchoring sites. The operative branches 360 and 362bend inward, toward the sheath axis 372, to place the electrode elements28 in contact with tissue spanning the anchoring sites.

[0302]FIG. 59 shows an alternative embodiment of a self-anchoringstructure 374. Like the structure 356 shown in FIG. 56, the structure374 includes two branches 376 and 378, which are slidably carried withina sheath 380. When deployed outside the sheath 380, the distal ends 384and 386 of the branches 376 and 378 are located in an outwardly bowedorientation relative to the axis 388 of the sheath 380. As earlierdescribed in connection with the FIG. 45 embodiment, the branches 376and 378 can be bent outwardly either by prestressing the associatedinterior spline elements 380, located in the branches 376 and 378, orproviding active steering, or both.

[0303] In FIG. 59, a flexible element 382 spans the distal ends 484 and386 of the branches 376 and 378. The flexible element 382 is made ofmaterial that is less rigid that the two branches 376 and 378. In theillustrated embodiment, the flexible element 382 is biased to assume anormally outwardly bowed shape, as FIG. 59 shows. The element 382carries one or more operative elements, which can vary and which in theillustrated embodiment comprise electrode elements 28.

[0304] As FIG. 60 shows, in use, each distal region 384 and 386 isintended to be individually maneuvered into spaced apart anchoringsites, e.g., the pulmonary veins (PV in FIG. 60). When the regions 384and 386 are suitably anchored, the spanning element 382 places theelectrode elements 28 in contact with tissue spanning the anchoringsites. If the tissue region between the anchoring sites has a concavecontour (and not a convex contour, as FIG. 60 shows), the outwardlybowed bias of the flexible element 382 will conform to the concavecontour, just as it conforms to a convex contour.

[0305] 4. Spring-Assisted Branch Structures

[0306]FIG. 61 shows another embodiment of a spring-assisted multipleelectrode structure 390. The structure 390 includes two operativebranches 392 and 394 carried at the distal end 16 of the catheter tube12. The catheter tube 12 forms part of a probe 10, as shown in FIG. 1.

[0307] As previously described in connection with the embodiment shownin FIG. 56, each operative branch 392 and 394 comprises a spline element396 enclosed within an electrically insulating sleeve 398. Operativeelements, for example, electrode elements 28, are carried by the sleeve398.

[0308] In the FIG. 61 embodiment, the spline elements 396 are preformedto move along the exterior of the distal catheter end 16 and then extendradially outward at an angle of less than 90°. The spline elements 396,prestressed in this condition, act as spring mechanisms for theoperative branches 392 and 394. The prestressed spline elements 396 holdthe branches 392 and 394 in a spaced apart condition (shown in FIG. 61),but resisting further or less radial separation of the branches 392 and394.

[0309] A sheath 400 is slidable in a forward direction (arrow 402 inFIG. 62) along the catheter tube 12 to press against and close theradial spacing between the branches 392 and 394. This low profilegeometry (shown in FIG. 62) allows introduction of the structure 390into the selected body region. Rearward movement of the sheath 400(arrow 404 in FIG. 61) frees the branches 392 and 394, which return dueto the spring action of the spline elements 396 to a normally spacedapart condition (shown in FIG. 61).

[0310] The catheter tube 12 includes an interior lumen 406. As FIG. 61shows, the lumen 406 accommodates passage of a guide wire 408 with ablunt distal end 410.

[0311] When deployed in an atrium (as FIG. 63A depicts) the distal end410 of the guide wire 408 is maneuvered into a selected anchoring site(e.g., a pulmonary vein in the left atrium, or the inferior vena cava inthe right atrium). The structure 390, enclosed within the sheath 400, isslid over the guide wire 408 to the targeted site (arrow 412 in FIG.63A). As FIG. 63B shows, the sheath 400 is moved rearwardly (arrow 414in FIG. 63B) to free the spring-like operative branches 392 and 394.Advancing the operative branches 392 and 394 along the guide wire 408opens the radial spacing between the branches. The spring action of thespline elements 396 resisting this action exerts force against thetissue, assuring intimate contact between the electrode elements 28 andthe tissue. The spline elements 396 can also be deployed within anatrium without use of a guide wire 408.

[0312] One or more spring-assisted spline elements 396 of the kind shownin FIG. 61 can also be deployed in a ventricle or in contact with theatrial septum for the purpose of making large lesions. As in the atrium,use of the guide wire 408 is optional. However, as shown in FIG. 63C, inthese regions, a guide wire 408 can be used, which includes at itsdistal end a suitable positive tissue fixation element 542, e.g., ahelical screw or vacuum port, to help stabilize the contact between thespline elements 396 and myocardial tissue. Several spline elements 396can be arranged in a circumferentially spaced star pattern to cover alarge surface area and thereby make possible the larger, deeper lesionsbelieved to be beneficial in the treatment of ventricular tachycardia.

[0313] The spring action (i.e., spring constant) of the spline elements396 can be varied, e.g., by changing the cross sectional area of thespline elements 396, or by making material composition or materialprocessing changes.

[0314] 5. Self-Anchoring Loop Structures

[0315]FIG. 66 shows an assembly 450, which, in use, creates aself-anchoring loop structure 452 (which is shown in FIG. 68). Theassembly 450 includes a catheter 486 comprising a flexible catheter tube454 with a handle 256 on its proximal end, and which carries a multipleelectrode array 458 on its distal end 470.

[0316] In the illustrated embodiment, the multiple electrode array 458comprises electrode elements 28 attached to a sleeve 460 (see FIG. 69),which is made from an electrically insulating material, as alreadydescribed.

[0317] As FIG. 69 best shows, a bendable spring 462 is carried withinthe sleeve 460 near the distal end 470 of the catheter tube 454. One ormore steering wires 464 are attached to the spring 462 and pass throughthe catheter tube 454 to a steering controller 468 in the handle. Whilevarious steering mechanisms can be used, in the illustrated embodiment,the controller 468 comprises a rotatable cam wheel of the type shown inLundquist and Thompson U.S. Pat. No. 5,254,088, which is alreadyincorporated into this Specification by reference.

[0318] Operation of the steering controller 468 pulls on the steeringwires 464 to apply bending forces to the spring 462. Bending of thespring 462 bends (arrows 490 in FIG. 66) the distal end 470 of thecatheter tube 454 (shown in phantom lines), to deflect the multipleelectrode array 458. As heretofore described, the catheter 486 cancomprise a conventional steerable catheter.

[0319] The catheter tube 454 carries a sheath 472. The sheath 472includes a proximal gripping surface 482 accessible to the physician.The sheath 472 also includes a closed distal end 476, and a slot 474,which is cut out proximal to the closed distal end 476. A region 480 ofthe sheath remains between the distal edge of the slot 474 and theclosed distal catheter tube end 476. This region 480 peripherallysurrounds an interior pocket 478.

[0320] The catheter tube 12 is slidable within the sheath 472. When thedistal end 470 occupies the slot 474, sliding the catheter tube 12forward inserts the distal end 470 into the pocket 478, as FIG. 67shows. The distal end 470 of the catheter tube 454 can be inserted intothe pocket 478 either before introduction of the electrode array 458into the targeted body region, or after introduction, when the electrodearray 458 is present within the targeted body region. The pocket 478 issized to snugly retain the inserted end 470 by friction or interference.

[0321] By holding the sheath 472 stationary and applying a rearwardsliding force on the catheter tube 454, the physician is able to freethe distal catheter tube end 470 from the pocket 478, as FIG. 66 shows.With the distal end 470 free of the pocket 478, the physician is able toslide the entire catheter tube 454 from the sheath 472, if desired, andinsert a catheter tube of another catheter in its place.

[0322] Once the distal catheter tube end 470 is inserted into the pocket478, the physician can form the loop structure 452. More particularly,by gripping the surface 482 to hold the sheath 472 stationary, thephysician can slide the catheter tube 454 forward with respect to thesheath 472 (arrow 484 in FIG. 68). As FIG. 68 shows, advancement of thecatheter tube 454 progressively pushes the multiple electrode array 458outward through the slot 474. With the distal end 470 captured withinthe pocket 478, the pushed-out portion of the electrode array 458 bendsand forms the loop structure 452.

[0323] In many respects, the loop structure 452 shown in FIG. 68 sharesattributes with the loop structure 20, shown in FIG. 3A. The sheathregion 488 underlying the slot 474 serves as a flexible joint for theloop structure 452, just as the flexible joint 44 does for the loopstructure 20 in FIG. 3A. However, unlike the structure 20 in FIG. 3A,the physician is able to mate with the pocket 478 a catheter of his/herown choosing, since the pocket 478 allows easy insertion and removal ofa catheter from the assembly 450. The physician is thereby given theopportunity to select among different catheter types and styles for usein forming the loop structure 452.

[0324] Furthermore, as FIG. 70 shows, the distal end 470 of the cathetertube 454, when retained within the pocket 478, can serve to establishcontact with an anatomic structure S, while the loop structure 452contacts nearby tissue T. As FIG. 67 shows, operation of the steeringcontroller 468 serves to deflect the pocket region 480 of the sheath 472along with the distal catheter tube end 470, to help maneuver and locatethe sheath distal end 470 in association with the anatomic structure S.The distal end 470 of the catheter tube 454, retained within the pocket478, can thereby serve to stabilize the position of the loop structure452 in contact with tissue T during use.

[0325] The stiffness of the sheath 472 and the length of the flexiblejoint region 488 are selected to provide mechanical properties to anchorthe loop structure 452 during use. Generally speaking, the sheath 472 ismade from a material having a greater inherent stiffness (i.e., greaterdurometer) than the structure 452 itself. The selected material for thesheath 472 can also be lubricious, to reduce friction during relativemovement of the catheter tube 454 within the sheath 472. For example,materials made from polytetrafluoroethylene (PTFE) can be used for thesheath 452. The geometry of the loop structure 452 can be altered byvarying the stiffness of the sheath 472, or varying the stiffness or thelength of the flexible joint 488, or one or more of these at the sametime.

[0326] There are various ways to enhance the releasable retention forcebetween the distal catheter tube end 470 and the pocket 478. Forexample, FIG. 71 shows a sheath 472 having a pocket region 480 in whichthe interior walls 500 of the pocket 478 are tapered to provide areleasable interference fit about the distal catheter tube end 470. Asanother example, FIG. 72 shows a distal catheter tube end 470, whichincludes a ball-nose fixture 502 which makes releasable, snap-fitengagement with a mating cylindrical receiver 504 formed in the pocket478. By providing active attachment mechanisms within the pocket 478,the effective length of the pocket region 480 can be reduced. Thesepreformed regions can be formed by thermal molding.

[0327]FIG. 73 shows a modification of the self-anchoring loop structure452 shown in FIG. 68, in which the distal end 470 of the catheter tube454 forms a pivoting junction 506 with the pocket region 480 of thesheath 472. FIGS. 74 and 75 show the details of one embodiment of thepivoting junction 506.

[0328] As FIG. 74 shows, the pocket region 480 includes an axial groove508 that opens into the pocket 478. The distal end 470 of the cathetertube includes a ball joint 510. As FIG. 75 shows, forward slidingmovement of the catheter tube 454 advances the distal end 470, includingthe ball joint 510, into the pocket 478. As FIG. 76 shows, as furtheradvancement of the catheter tube 454 progressively pushes the multipleelectrode array 458 outward through the slot 474, the ball joint 510enters the groove 508. The ball joint 510 pivots within the groove 508,thereby forming the pivoting junction 506. The junction 506 allows thedistal end 470 to swing with respect to the pocket region 480 (arrows512 in FIG. 76), as the pushed-out portion of the electrode array 458bends and forms the loop structure 452, shown in FIG. 73.

[0329]FIGS. 77A to 77D show another embodiment of the pivoting junction506. In this embodiment, a separately cast plastic or metal cap 514 isattached to the end of the sheath 472. The cap 514 includes an interiorcavity forming the pocket 478. Unlike the previously describedembodiments, the pocket 478 in the cap 514 includes an interior wall 516(see FIG. 77D), which is closed except for a slotted keyway 518.

[0330] The cap 514 includes the previously described groove 508. Unlikethe previous embodiments, the groove 508 extends to and joins theslotted keyway 518 (see FIG. 77A). The groove 508 also extends throughthe distal end 520 of the cap 514 to an opening 522 (see FIG. 77B) onthe side of the cap 514 that faces away from the sheath slot 474. AsFIG. 77B shows, the opening 522 accommodates passage of the ball joint510 carried at the distal end 470 of the catheter tube 454. Advancingthe ball joint 510 from the opening 522 along the groove 508 locks theball joint 510 within the pocket 478. Further advancement brings theball joint 510 to rest within the slotted keyway 518 (see FIG. 77C). Theslotted keyway 518 retains the ball joint 510, securing the distalcatheter tube end 470 to the cap 514. The interference between the balljoint 510 and the keyway 518 prevents separation of the distal cathetertube end 470 from the sheath 472 by sliding axial movement of thecatheter tube 545 within the sheath 472. However, as FIG. 77D shows, theball joint 510 pivots within the groove 508 of the cap 514, therebyforming the pivoting junction 506, to allow the distal end 470 to swingwith respect to the pocket region 478.

[0331] The distal catheter tube end 470 is separated from the cap 514 bysliding the ball joint 510 along the groove 508 into the opening 522.The ball joint 510 passes through the opening 522, thereby releasing thecatheter tube 454 from the sheath 472.

[0332]FIGS. 78A to 78C show another embodiment of the pivoting junction506. In this embodiment, like FIGS. 77A to 77D, a separately castplastic or metal cap 606 is attached to the end of the sheath 472. Thecap 606 includes an interior cavity forming the pocket 608. As FIG. 78Ashows, the pocket 608 receives the ball joint 510 (carried by the distalloop structure end 470) through the sheath end 612 of the cap 606, inthe manner previously described and shown with reference to FIG. 76.

[0333] As FIGS. 78B and 78C show, the ball joint 510 pivots within thepocket 608 through a groove 610 formed in the cap 514. The pivotingjunction 506 is thereby formed, which allows the distal end 470 to swingwith respect to the cap 606.

[0334] 6. Deployment and Use of Self-Anchoring Multiple ElectrodeStructures

[0335] 1. Left Atrium

[0336] The self-anchoring multiple electrode structures described abovecan be deployed into the left atrium to create lesions between thepulmonary veins and the mitral valve annulus. Tissue nearby theseanatomic structures are recognized to develop arrhythmia substratescausing atrial fibrillation. Lesions in these tissue regions blockreentry paths or destroy active pacemaker sites, and thereby prevent thearrhythmia from occurring.

[0337]FIG. 79 shows (from outside the heart H) the location of the majoranatomic landmarks for lesion formation in the left atrium. Thelandmarks include the right inferior pulmonary vein (RIPV), the rightsuperior pulmonary vein (RSPV), the left superior pulmonary vein (LSPV),the left inferior pulmonary vein (LIPV); and the mitral valve annulus(MVA). FIGS. 80A to FIGS. 80D show representative lesion patterns formedinside the left atrium based upon these landmarks.

[0338] In FIG. 80A, the lesion pattern comprises a first leg L1 betweenthe right inferior pulmonary vein (RIPV) and the right superiorpulmonary vein (RSPV); a second leg L2 between the RSPV and the leftsuperior pulmonary vein (LSPV); a third leg L3 between the left superiorpulmonary vein (LSPV) and the left inferior pulmonary vein (LIPV); and afourth leg L4 leading between the LIPV and the mitral valve annulus(MVA).

[0339]FIG. 80B shows an intersecting lesion pattern comprisinghorizontal leg L1 extending between the RSPV-LSPV on one side and theRIPV-LIPV on the other size, intersected by vertical leg L2 extendingbetween the RSPV-RIPV on one side and the LSPV-LIPV on the other side.The second leg L2 also extends to the MVA.

[0340]FIG. 80C shows a criss-crossing lesion pattern comprising a firstleg extending between the RSPV and LIPV; a second leg L2 extendingbetween the LSPV and RIPV; and a third leg L3 extending from the LIPV tothe MVA.

[0341]FIG. 80D shows a circular lesion pattern comprising a leg L1 thatextends from the LSPV, and encircles to RSPV, RIPV, and LIPV, leadingback to the LSPV.

[0342] The linear lesion patterns shown in FIGS. 80A, 80B, and 80C canbe formed, e.g., using the structure 272 shown in FIGS. 45 and 46, byplacing the anchoring branch 276 in a selected one of the pulmonaryveins to stabilize the position of the operative branch 274, and thenmaneuvering the operative branch 274 to sequentially locate it along thedesired legs of the lesion pattern. It may be necessary to relocate theanchoring branch 276 in a different pulmonary vein to facilitatemaneuvering of the operative branch 274 to establish all legs of thepattern. The branched structures 356 (FIG. 56) or 374 (FIG. 59) can alsobe used sequentially for the same purpose, in the manner shown in FIG.58 (for structure 356) and FIG. 60 (for structure 374).

[0343] The circular lesion pattern shown in FIG. 80D can be formed,e.g., using an anchored loop structure 458 as shown in FIG. 68 or 73.Using these structures, the distal end 470 of the catheter tube 454(enclosed within the pocket 478) is located within a selected one of thepulmonary veins (the LSPV in FIG. 80D), and the loop structure isadvanced from the sheath 472 to circumscribe the remaining pulmonaryveins. As with other loop structures, the loop structure tend to seekthe largest diameter and occupy it. Most of the structures are suitablefor being torqued or rotated into other planes and thereby occupysmaller regions. The anchored loop structure 458 is also suited forforming lesion legs that extend from the inferior pulmonary veins to themitral valve annulus (for example, L4 in FIG. 80A and L3 in FIG. 80C).

[0344] To access the left atrium, any of these structures can beintroduced in the manner shown in FIG. 44 through the inferior vena cava(IVC) into the right atrium, and then into the left atrium through aconventional transeptal approach. Alternatively, a retrograde approachcan be employed through the aorta into the left ventricle, and thenthrough the mitral valve into the left atrium.

[0345] 2. Right Atrium

[0346]FIG. 79 shows (from outside the heart H) the location of the majoranatomic landmarks for lesion formation in the right atrium. Theselandmarks include the superior vena cava (SVC), the tricuspid valveannulus (TVA), the inferior vena cava (IVC), and the coronary sinus(CS). Tissue nearby these anatomic structures have been identified asdeveloping arrhythmia substrates causing atrial fibrillation. Lesions inthese tissue regions block reentry paths or destroy active pacemakersites and thereby prevent the arrhythmia from occurring.

[0347]FIGS. 81A to 81C show representative lesion patterns formed insidethe right atrium based upon these landmarks.

[0348]FIG. 81A shows a representative lesion pattern L that extendsbetween the superior vena cava (SVC) and the tricuspid valve annulus(TVA).

[0349]FIG. 81B shows a representative lesion pattern that extendsbetween the interior vena cava (IVC) and the TVA. FIG. 81C shows arepresentative lesion pattern L that extends between the coronary sinus(CS) and the tricuspid valve annulus (TVA).

[0350] The self-anchoring multiple electrode structures described abovecan be deployed into the right atrium to create these lesions. Forexample, the structure 272 shown in FIGS. 45 and 46 can be used, byplacing the anchoring branch 276 in the SVC or IVC to stabilize theposition of the operative branch 274, and then maneuvering the operativebranch 274 to locate it along the desired path of the lesion pattern.The branched structures 356 (FIG. 56) or 374 (FIG. 59) can also be usedsequentially for the same purpose, in the manner shown in FIG. 58 (forstructure 356) and FIG. 60 (for structure 374).

[0351] Any of these structures can be introduced in the manner shown inFIG. 44 through the inferior vena cava (IVC) into the right atrium.

[0352] 3. Epicardial Use

[0353] Many of the structures suited for intracardiac deployment, asdiscussed above, can be directly applied to the epicardium throughconventional thoracotomy or thoracostomy techniques. For example, thestructures shown in FIGS. 56, 59, 61, 66, and 73 are well suited forepicardial application.

[0354] III. Flexible Electrode Structures

[0355] A. Spacing of Electrode Elements

[0356] In the illustrated embodiment, the size and spacing of theelectrode elements 28 on the various structures can vary.

[0357] 1. Long Lesion Patterns

[0358] For example, the electrode elements 28 can be spaced and sizedfor creating continuous, long lesion patterns in tissue, as exemplifiedby the lesion pattern 418 in tissue T shown in FIG. 64. Long, continuouslesion patterns 418 are beneficial to the treatment of atrialfibrillation. The patterns 418 are formed due to additive heatingeffects, which cause the lesion patterns 418 to span adjacent, spacedapart electrode 28, creating the desired elongated, long geometry, asFIG. 64 shows.

[0359] The additive heating effects occur when the electrode elements 28are operated simultaneously in a bipolar mode between electrode elements28. Furthermore, the additive heating effects also arise when theelectrode elements 28 are operated simultaneously in a unipolar mode,transmitting energy to an indifferent electrode 420 (shown in FIG. 44).

[0360] More particularly, when the spacing between the electrodes 28 isequal to or less than about 3 times the smallest of the diameters of theelectrodes 28, the simultaneous emission of energy by the electrodes 28,either bipolar between the segments or unipolar to the indifferentelectrode 420, creates an elongated continuous lesion pattern 58 in thecontacted tissue area due to the additive heating effects.

[0361] Alternatively, when the spacing between the electrodes along thecontacted tissue area is equal to or less than about 2 times the longestof the lengths of the electrodes 28, the simultaneous application ofenergy by the electrodes 28, either bipolar between electrodes 28 orunipolar to the indifferent electrode 420, also creates an elongatedcontinuous lesion pattern 58 in the contacted tissue area due toadditive heating effects.

[0362] Further details of the formation of continuous, long lesionpatterns are found in copending U.S. patent application Ser. No.08/287,192, filed Aug. 8, 1994, entitled “Systems and Methods forForming Elongated Lesion Patterns in Body Tissue Using Straight orCurvilinear Electrode Elements,” which is incorporated herein byreference.

[0363] Alternatively, long continuous lesion patterns, like that shownin FIG. 64, can be achieved using an elongated electrode element madefrom a porous material. By way of illustration, FIG. 82 shows a loopelectrode structure 424, like that shown in FIG. 2A. The structure 424includes an electrode body 428, which includes a porous material 430 totransfer ablation energy by ionic transport.

[0364] As FIG. 82 shows, the distal end 426 of the electrode body 428 iscoupled to a flexible joint 440, which is part of the slotted sheath442, as previously described in connection with FIG. 3A. Advancement ofthe electrode body 428 from the slotted sheath 442 creates the loopstructure 424, in the same manner that the loops structure 20 shown inFIG. 3A is formed.

[0365] As best shown in FIG. 83, the electrode body 428 includes acenter support lumen 432 enveloped by the porous material 430. The lumen432 carries spaced-apart electrodes 429 along its length. The lumen 432also includes spaced-apart apertures 434 along its length.

[0366] The lumen 432 includes a proximal end 430, which communicateswith a source of ionic fluid 438. The lumen 432 conveys the ionic fluid438. The ionic fluid 438 passes through the apertures 434 and fills thespace between the lumen 432 and the surrounding porous material 430. Thefluid 438 also serves to expand the diameter of the structure 424. Thestructure 424 therefore possesses a low profile geometry, when no liquid438 is present, for introduction within the targeted body regionenclosed within the slotted sheath 442. Once advanced from the sheath442 and formed into the loop structure 424, fluid 438 can be introducedto expand the structure 424 for use.

[0367] The porous material 430 has pores capable of allowing transportof ions contained in the fluid 438 through the material 430 and intocontact with tissue. As FIG. 83 also shows, the electrodes 429 arecoupled to a source 444 of radio frequency energy. The electrodes 429transmit the radio frequency energy into the ionic fluid 438. The ionic(and, therefore, electrically conductive)fluid 438 establishes anelectrically conductive path. The pores of the porous material 430establish ionic transport of ablation energy from the electrodes 429,through the fluid 438, liquid, to tissue outside the electrode body 428.

[0368] Preferably, the fluid 438 possesses a low resistivity to decreaseohmic loses, and thus ohmic heating effects, within the body 428. Thecomposition of the electrically conductive fluid 438 can vary. In theillustrated embodiment, the fluid 438 comprises a hypertonic salinesolution, having a sodium chloride concentration at or near saturation,which is about 5% to about 25% weight by volume. Hypertonic salinesolution has a low resistivity of only about 5 ohm·cm, compared to bloodresistivity of about 150 ohm·cm and myocardial tissue resistivity ofabout 500 ohm·cm.

[0369] Alternatively, the composition of the electrically conductivefluid 438 can comprise a hypertonic potassium chloride solution. Thismedium, while promoting the desired ionic transfer, requires closermonitoring of the rate at which ionic transport occurs through the poresof the material 430, to prevent potassium overload. When hypertonicpotassium chloride solution is used, it is preferred to keep the ionictransport rate below about 10 mEq/min.

[0370] Regenerated cellulose membrane materials, typically used forblood oxygenation, dialysis, or ultrafiltration, can be used as theporous material 430. Regenerated cellulose is electricallynon-conductive; however, the pores of this material (typically having adiameter smaller than about 0.1 μm) allow effective ionic transport inresponse to the applied RF field. At the same time, the relatively smallpores prevent transfer of macromolecules through the material 430, sothat pressure driven liquid perfusion is less likely to accompany theionic transport, unless relatively high pressure conditions developwithin the body 428.

[0371] Other porous materials can be used as the porous material 430.Candidate materials having pore sizes larger than regenerated cellulousmaterial, such as nylon, polycarbonate, polyvinylidene fluoride (PTFE),polyethersulfone, modified acrylic copolymers, and cellulose acetate,are typically used for blood microfiltration and oxygenation. Porous ormicroporous materials may also be fabricated by weaving a material (suchas nylon, polyester, polyethylene, polypropylene, fluorocarbon, finediameter stainless steel, or other fiber) into a mesh having the desiredpore size and porosity. These materials permit effective passage of ionsin response to the applied RF field. However, as many of these materialspossess larger pore diameters, pressure driven liquid perfusion, and theattendant transport of macromolecules through the pores, are also morelikely to occur at normal inflation pressures for the body 428.Considerations of overall porosity, perfusion rates, and lodgment ofblood cells within the pores of the body 128 must be taken more intoaccount as pore size increase.

[0372] Low or essentially no liquid perfusion through the porous body428 is preferred. Limited or essentially no liquid perfusion through theporous body 428 is beneficial for several reasons. First, it limits saltor water overloading, caused by transport of the hypertonic solutioninto the blood pool. This is especially true, should the hypertonicsolution include potassium chloride, as observed above. Furthermore,limited or essentially no liquid perfusion through the porous body 428allows ionic transport to occur without disruption. When undisturbed byattendant liquid perfusion, ionic transport creates a continuous virtualelectrode at the electrode body-tissue interface. The virtual electrodeefficiently transfers RF energy without need for an electricallyconductive metal surface.

[0373]FIGS. 84 and 85 show an embodiment of the porous electrode body428 which includes spaced-apart external rings 446, which form porouselectrode segments. It is believed that, as the expanded dimension ofthe body 428 approaches the dimension of the interior electrodes 429,the need to segment the electrode body 428 diminishes.

[0374] Alternatively, as FIG. 86 shows, instead of a lumen 432 withinthe body 438, a foam cylinder 448 coupled in communication with theionic fluid 438 could be used to carry the electrodes 429 and perfusethe ionic fluid 438.

[0375] 2. Interrupted Lesion Patterns

[0376] The electrode elements 28 can be sized and spaced to forminterrupted, or segmented lesion patterns, as exemplified by the lesionpattern 422 in tissue T shown in FIG. 65. Alternatively, spaced-apartelectrode elements 28 capable of providing long lesion patterns 418 canbe operated with some electrode elements 28 energized and others not, toprovide an interrupted lesion pattern 422, as FIG. 65 exemplifies.

[0377] When the spacing between the electrodes 28 is greater than about5 times the smallest of the diameters of the electrodes 28, thesimultaneous emission of energy by the electrodes 28, either bipolarbetween segments or unipolar to the indifferent electrode 420, does notgenerate additive heating effects. Instead, the simultaneous emission ofenergy by the electrodes 28 creates an elongated segmented, orinterrupted, lesion pattern in the contacted tissue area.

[0378] Alternatively, when the spacing between the electrodes 28 alongthe contacted tissue area is greater than about 3 times the longest ofthe lengths of the electrodes 28, the simultaneous application ofenergy, either bipolar between electrodes 28 or unipolar to theindifferent electrode 420, creates an elongated segmented, orinterrupted, lesion pattern.

[0379] 3. Flexibility

[0380] When the electrode elements 28 are flexible, each element 28 canbe as long as 50 mm. Thus, if desired, a single coil electrode element28 can extend uninterrupted along the entire length of the supportstructure. However, a segmented pattern of spaced apart, shorterelectrode elements 28 is preferred.

[0381] If rigid electrode elements 28 are used, the length of the eachelectrode segment can vary from about 2 mm to about 10 mm. Usingmultiple rigid electrode elements 28 longer than about 10 mm eachadversely effects the overall flexibility of the element. Generallyspeaking, adjacent electrode elements 28 having lengths of less thanabout 2 mm do not consistently form the desired continuous lesionpatterns.

[0382] 4. Temperature Sensing

[0383] As FIG. 3A shows, each electrode element 28 can carry at leastone and, preferably, at least two, temperature sensing elements 540. Themultiple temperature sensing elements 540 measure temperatures along thelength of the electrode element 28. The temperature sensing elements 540can comprise thermistors or thermocouples. If thermocouples are used, acold junction 24 (see FIG. 3A) can be carried on the same structure asthe electrode elements 28.

[0384] An external temperature processing element (not shown) receivesand analyses the signals from the multiple temperature sensing elements540 in prescribed ways to govern the application of ablating energy tothe electrode element 28. The ablating energy is applied to maintaingenerally uniform temperature conditions along the length of the element28.

[0385] Further details of the use of multiple temperature sensingelements in tissue ablation can be found in copending U.S. patentapplication Ser. No. 08/286,930, filed Aug. 8, 1994, entitled “Systemsand Methods for Controlling Tissue Ablation Using Multiple TemperatureSensing Elements.”

[0386] Various features of the invention are set forth in the followingclaims.

We claim:
 1. A catheter assembly comprising a elongated, flexiblesupport structure having an axis, and an elongated porous electrodeassembly carried by the support structure along the axis for contactwith tissue, the elongated porous electrode assembly comprising a wallhaving an exterior peripherally surrounding an interior area, a lumen toconvey a medium containing ions into the interior area, and an elementcoupling the medium within the interior area to a source of electricalenergy, at least a portion of the wall comprising a porous materialsized to allow passage of ions contained in the medium to thereby enableionic transport of electrical energy through the porous material to theexterior of the wall to form a continuous elongated lesion pattern intissue contacted by the wall.
 2. A catheter assembly according to claim1 wherein the elongated porous electrode assembly comprises an array ofelectrode segments formed by segmenting the wall along the axis.
 3. Acatheter assembly according to claim 1 wherein the support structure hasa curvilinear geometry, and wherein the elongated porous electrodeassembly conforms to the curvilinear geometry.
 4. A catheter assemblyaccording to claim 1 wherein the support structure is adapted to form aloop geometry, and wherein the elongated porous electrode assemblyconforms to the loop geometry.
 5. A catheter assembly according to claim1 wherein the porous material comprises a microporous membrane.
 6. Acatheter assembly according to claim 1 wherein the porous materialcomprises an ultrafiltration membrane.
 7. A catheter assembly accordingto claim 1 wherein the element comprises an electrically conductiveelectrode in the interior area of the wall.
 8. A catheter assemblyaccording to claim 1 wherein the medium comprises a hypertonic solution.9. A catheter assembly according to claim 1 wherein the porous materialis sized to pass ions contained in the medium without substantial liquidperfusion through the porous material.